Also failed on:
https://ci.chromium.org/buildbot/internal.client.clank/x64-builder/

The error on many of the looks like:

/b/build/slave/goma_cache/client/gomacc ../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/v8/v8_base/serializer.o.d -DV8_DEPRECATION_WARNINGS -DNO_TCMALLOC -DSAFE_BROWSING_DB_REMOTE -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -D_GNU_SOURCE -DANDROID -DHAVE_SYS_UIO_H -DANDROID_NDK_VERSION_ROLL=r16_1 -DCR_CLANG_REVISION=\"348507-1\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS -DCR_LIBCXX_REVISION=349080 -DCR_LIBCXXABI_REVISION=347903 -D_LIBCPP_ABI_UNSTABLE -D_LIBCPP_ENABLE_NODISCARD -D__GNU_SOURCE=1 -DCHROMIUM_CXX_TWEAK_INLINES -D_DEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1 -DENABLE_DISASSEMBLER -DV8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=64 -DENABLE_MINOR_MC -DOBJECT_PRINT -DVERIFY_HEAP -DV8_TRACE_MAPS -DV8_ENABLE_ALLOCATION_TIMEOUT -DV8_ENABLE_FORCE_SLOW_PATH -DV8_ENABLE_CHECKS -DV8_DEPRECATION_WARNINGS -DV8_INTL_SUPPORT -DENABLE_HANDLE_ZAPPING -DV8_USE_SNAPSHOT -DV8_USE_EXTERNAL_STARTUP_DATA -DV8_CONCURRENT_MARKING -DV8_EMBEDDED_BUILTINS -DV8_TARGET_ARCH_X64 -DDEBUG -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DUSE_CHROMIUM_ICU=1 -DU_STATIC_IMPLEMENTATION -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=uint16_t -I../.. -Igen -I../../v8 -Igen/v8 -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../v8/include -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -fcolor-diagnostics -fmerge-all-constants -Xclang -mllvm -Xclang -instcombine-lower-dbg-declare=0 -Xclang -fdebug-compilation-dir -Xclang . -no-canonical-prefixes -fcomplete-member-pointers -ffunction-sections -fno-short-enums --target=x86_64-linux-android -isystem../../third_party/android_ndk/sysroot/usr/include/x86_64-linux-android -D__ANDROID_API__=21 -m64 -march=x86-64 -Wall -Werror -Wextra -Wimplicit-fallthrough -Wthread-safety -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-unneeded-internal-declaration -Wno-undefined-var-template -Wno-null-pointer-arithmetic -Wno-ignored-pragma-optimize -fomit-frame-pointer -g1 -fdebug-info-for-profiling -fvisibility=hidden -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so -Xclang -add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs -Xclang enforce-in-thirdparty-webkit -Xclang -plugin-arg-find-bad-constructs -Xclang check-enum-max-value -Xclang -plugin-arg-find-bad-constructs -Xclang check-ipc -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wexit-time-destructors -Wmissing-field-initializers -Winconsistent-missing-override -Wunreachable-code -Wshorten-64-to-32 -O2 -fno-ident -fdata-sections -ffunction-sections -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare -std=c++14 -fno-exceptions -fno-rtti -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include --sysroot=../../third_party/android_ndk/sysroot -isystem../../third_party/android_ndk/sources/android/support/include -fvisibility-inlines-hidden -c ../../v8/src/snapshot/serializer.cc -o obj/v8/v8_base/serializer.o
clang++: /b/swarming/w/ir/kitchen-workdir/src/third_party/llvm/lib/Target/X86/X86DiscriminateMemOps.cpp:119: virtual bool (anonymous namespace)::X86DiscriminateMemOps::runOnMachineFunction(llvm::MachineFunction &): Assertion `MustInsert.second && "New discriminator shouldn't be present in set"' failed.
Stack dump:
0.	Program arguments: ../../third_party/llvm-build/Release+Asserts/bin/clang++ -cc1 -triple x86_64-unknown-linux-android -emit-obj -disable-free -main-file-name serializer.cc -mrelocation-model pic -pic-level 2 -mthread-model posix -fmerge-all-constants -relaxed-aliasing -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -target-feature +sse4.2 -target-feature +popcnt -fdebug-info-for-profiling -dwarf-column-info -debug-info-kind=line-tables-only -dwarf-version=4 -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -coverage-notes-file /b/build/slave/x64-builder/build/src/out/Debug/obj/v8/v8_base/serializer.gcno -nostdinc++ -resource-dir ../../third_party/llvm-build/Release+Asserts/lib/clang/8.0.0 -dependency-file obj/v8/v8_base/serializer.o.d -MT obj/v8/v8_base/serializer.o -isystem ../../third_party/android_ndk/sysroot/usr/include/x86_64-linux-android -isystem ../../buildtools/third_party/libc++/trunk/include -isystem ../../buildtools/third_party/libc++abi/trunk/include -isystem ../../third_party/android_ndk/sources/android/support/include -D V8_DEPRECATION_WARNINGS -D NO_TCMALLOC -D SAFE_BROWSING_DB_REMOTE -D CHROMIUM_BUILD -D FIELDTRIAL_TESTING_ENABLED -D _GNU_SOURCE -D ANDROID -D HAVE_SYS_UIO_H -D ANDROID_NDK_VERSION_ROLL=r16_1 -D CR_CLANG_REVISION="348507-1" -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D _LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS -D CR_LIBCXX_REVISION=349080 -D CR_LIBCXXABI_REVISION=347903 -D _LIBCPP_ABI_UNSTABLE -D _LIBCPP_ENABLE_NODISCARD -D __GNU_SOURCE=1 -D CHROMIUM_CXX_TWEAK_INLINES -D _DEBUG -D DYNAMIC_ANNOTATIONS_ENABLED=1 -D WTF_USE_DYNAMIC_ANNOTATIONS=1 -D ENABLE_DISASSEMBLER -D V8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=64 -D ENABLE_MINOR_MC -D OBJECT_PRINT -D VERIFY_HEAP -D V8_TRACE_MAPS -D V8_ENABLE_ALLOCATION_TIMEOUT -D V8_ENABLE_FORCE_SLOW_PATH -D V8_ENABLE_CHECKS -D V8_DEPRECATION_WARNINGS -D V8_INTL_SUPPORT -D ENABLE_HANDLE_ZAPPING -D V8_USE_SNAPSHOT -D V8_USE_EXTERNAL_STARTUP_DATA -D V8_CONCURRENT_MARKING -D V8_EMBEDDED_BUILTINS -D V8_TARGET_ARCH_X64 -D DEBUG -D U_USING_ICU_NAMESPACE=0 -D U_ENABLE_DYLOAD=0 -D USE_CHROMIUM_ICU=1 -D U_STATIC_IMPLEMENTATION -D ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -D UCHAR_TYPE=uint16_t -I ../.. -I gen -I ../../v8 -I gen/v8 -I ../../third_party/icu/source/common -I ../../third_party/icu/source/i18n -I ../../v8/include -D __DATE__= -D __TIME__= -D __TIMESTAMP__= -D __ANDROID_API__=21 -isysroot ../../third_party/android_ndk/sysroot -internal-isystem ../../third_party/android_ndk/sysroot/usr/local/include -internal-isystem ../../third_party/llvm-build/Release+Asserts/lib/clang/8.0.0/include -internal-externc-isystem ../../third_party/android_ndk/sysroot/usr/include/x86_64-linux-android -internal-externc-isystem ../../third_party/android_ndk/sysroot/include -internal-externc-isystem ../../third_party/android_ndk/sysroot/usr/include -O2 -Wno-builtin-macro-redefined -Wall -Werror -Wextra -Wimplicit-fallthrough -Wthread-safety -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-unneeded-internal-declaration -Wno-undefined-var-template -Wno-null-pointer-arithmetic -Wno-ignored-pragma-optimize -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wexit-time-destructors -Wmissing-field-initializers -Winconsistent-missing-override -Wunreachable-code -Wshorten-64-to-32 -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare -std=c++14 -fdeprecated-macro -fdebug-compilation-dir /b/build/slave/x64-builder/build/src/out/Debug -ferror-limit 19 -fmessage-length 0 -fvisibility hidden -fvisibility-inlines-hidden -stack-protector 1 -stack-protector-buffer-size 4 -fno-rtti -fobjc-runtime=gcc -Qn -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -mllvm -instcombine-lower-dbg-declare=0 -fdebug-compilation-dir . -load ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so -add-plugin find-bad-constructs -plugin-arg-find-bad-constructs enforce-in-thirdparty-webkit -plugin-arg-find-bad-constructs check-enum-max-value -plugin-arg-find-bad-constructs check-ipc -o obj/v8/v8_base/serializer.o -x c++ ../../v8/src/snapshot/serializer.cc -fcomplete-member-pointers -faddrsig 
1.	<eof> parser at end of file
2.	Code generation
3.	Running pass 'Function Pass Manager' on module '../../v8/src/snapshot/serializer.cc'.
4.	Running pass 'X86 Discriminate Memory Operands' on function '@_ZN2v88internal10Serializer16OutputStatisticsEPKc'
#0 0x0000000002211e44 (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x2211e44)
#1 0x000000000220fcee llvm::sys::RunSignalHandlers() (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x220fcee)
#2 0x0000000002212008 (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x2212008)
#3 0x00007f7a6406a330 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x10330)
#4 0x00007f7a62e82c37 gsignal /build/eglibc-ripdx6/eglibc-2.19/signal/../nptl/sysdeps/unix/sysv/linux/raise.c:56:0
#5 0x00007f7a62e86028 abort /build/eglibc-ripdx6/eglibc-2.19/stdlib/abort.c:91:0
#6 0x00007f7a62e7bbf6 __assert_fail_base /build/eglibc-ripdx6/eglibc-2.19/assert/assert.c:92:0
#7 0x00007f7a62e7bca2 (/lib/x86_64-linux-gnu/libc.so.6+0x2fca2)
#8 0x00000000013cb84d (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x13cb84d)
#9 0x000000000190940a llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x190940a)
#10 0x0000000001c716d9 llvm::FPPassManager::runOnFunction(llvm::Function&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x1c716d9)
#11 0x0000000001c71978 llvm::FPPassManager::runOnModule(llvm::Module&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x1c71978)
#12 0x0000000001c71f9a llvm::legacy::PassManagerImpl::run(llvm::Module&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x1c71f9a)
#13 0x00000000023dfb3c clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x23dfb3c)
#14 0x0000000002c6b06f (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x2c6b06f)
#15 0x00000000028fbb0c clang::MultiplexConsumer::HandleTranslationUnit(clang::ASTContext&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x28fbb0c)
#16 0x0000000003498ed3 clang::ParseAST(clang::Sema&, bool, bool) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x3498ed3)
#17 0x00000000028c69a0 clang::FrontendAction::Execute() (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x28c69a0)
#18 0x000000000286b091 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x286b091)
#19 0x000000000295f6dd clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x295f6dd)
#20 0x000000000090dee8 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x90dee8)
#21 0x000000000090b6e5 main (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x90b6e5)
#22 0x00007f7a62e6df45 __libc_start_main /build/eglibc-ripdx6/eglibc-2.19/csu/libc-start.c:321:0
#23 0x00000000009087ed _start (../../third_party/llvm-build/Release+Asserts/bin/clang+++0x9087ed)
clang++: error: unable to execute command: Aborted (core dumped)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 8.0.0 (trunk 348507)
Target: x86_64-unknown-linux-android
Thread model: posix
InstalledDir: ../../third_party/llvm-build/Release+Asserts/bin
clang++: note: diagnostic msg: PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace, preprocessed source, and associated run script.
clang++: note: diagnostic msg: 

And some of the CL ranges for first failure appear to include:

Roll clang 346388:348507.
https://chromium.googlesource.com/chromium/src/+/bd324208d892ab793b062049b1bd642bcee631d2

+thakis, +hans could this be related?

First failure on both:

https://ci.chromium.org/buildbot/chromium.android/Android%20Cronet%20x86%20Builder%20%28dbg%29/102286
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Android%20x64%20Builder%20%28dbg%29/31679

Have exactly that single cl in common, proceeding with revert.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f744168e409f017648ae5673c174b79e88fe26fd

commit f744168e409f017648ae5673c174b79e88fe26fd
Author: Juan Antonio Navarro Pérez <perezju@chromium.org>
Date: Thu Dec 20 11:56:56 2018

Revert "Roll clang 346388:348507."

This reverts commit bd324208d892ab793b062049b1bd642bcee631d2.

Reason for revert: Causing compile failures on multiple builders

Original change's description:
> Roll clang 346388:348507.
> 
> Bug:  904337 
> Change-Id: Icbc3e6fda8bcbaabedc0c823b91395dab3daf28b
> Reviewed-on: https://chromium-review.googlesource.com/c/1366078
> Reviewed-by: Hans Wennborg <hans@chromium.org>
> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#618154}

TBR=thakis@chromium.org,hans@chromium.org

Change-Id: Ib78eb22439b34da425a15478dfe88ee41c0b08a5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  904337 ,  916951 
Reviewed-on: https://chromium-review.googlesource.com/c/1386584
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618177}
[modify] https://crrev.com/f744168e409f017648ae5673c174b79e88fe26fd/tools/clang/scripts/update.py

Got a couple green builds on:
https://ci.chromium.org/buildbot/chromium.android/Android%20Cronet%20x86%20Builder%20%28dbg%29/