UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:62.0) Gecko/20100101 Firefox/62.0

Steps to reproduce the problem:
Build Chromium Linux for mipsel using LLVM revision 345419

1. build Clang version 345419 using tools/clang/scripts/update.py script
2. gn gen out/mips32r2 --args=" target_os=\"linux\" target_cpu=\"mipsel\" mips_arch_variant=\"r2\" is_debug=false"
3. ninja -C out/mips32r2 -j8 all

What is the expected behavior?
Chromium build should finish.

What went wrong?
Chromium build fails with error message:

[44408/78703] CXX clang_x86_v8_mipsel/obj/mojo/core/impl_for_embedder/channel.o
FAILED: clang_x86_v8_mipsel/obj/mojo/core/impl_for_embedder/channel.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF clang_x86_v8_mipsel/obj/mojo/core/impl_for_embedder/channel.o.d -DMOJO_SYSTEM_IMPL_IMPLEMENTATION -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_GNU_SOURCE -DCR_CLANG_REVISION=\"344066-1\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS -DCR_LIBCXX_REVISION=344254 -DCR_LIBCXXABI_REVISION=344215 -D_LIBCPP_ENABLE_NODISCARD -DCR_SYSROOT_HASH=9e6279438ece6fb42b5333ca90d5e9d0c188a403 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_32 -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_26 -I../.. -Iclang_x86_v8_mipsel/gen -I../../third_party/boringssl/src/include -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -B../../third_party/binutils/Linux_x64/Release/bin -pthread -fcolor-diagnostics -fmerge-all-constants -Xclang -mllvm -Xclang -instcombine-lower-dbg-declare=0 -no-canonical-prefixes -fcomplete-member-pointers -m32 -msse2 -mfpmath=sse -mmmx -momit-leaf-frame-pointer -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 -Wno-defaulted-function-deleted -O2 -fno-ident -fdata-sections -ffunction-sections -fno-omit-frame-pointer -g0 -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 -isystem../../build/linux/debian_sid_i386-sysroot/usr/include/glib-2.0 -isystem../../build/linux/debian_sid_i386-sysroot/usr/lib/i386-linux-gnu/glib-2.0/include -std=c++14 -fno-exceptions -fno-rtti -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include --sysroot=../../build/linux/debian_sid_i386-sysroot -fvisibility-inlines-hidden -c ../../mojo/core/channel.cc -o clang_x86_v8_mipsel/obj/mojo/core/impl_for_embedder/channel.o
In file included from ../../mojo/core/channel.cc:20:
In file included from ../../mojo/core/core.h:19:
In file included from ../../mojo/core/dispatcher.h:24:
../../mojo/public/c/system/buffer.h:33:1: error: static_assert failed "int64_t has weird alignment"
MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../mojo/public/c/system/macros.h:15:39: note: expanded from macro 'MOJO_STATIC_ASSERT'
#define MOJO_STATIC_ASSERT(expr, msg) static_assert(expr, msg)
                                      ^             ~~~~
In file included from ../../mojo/core/channel.cc:20:
In file included from ../../mojo/core/core.h:19:
In file included from ../../mojo/core/dispatcher.h:25:
../../mojo/public/c/system/data_pipe.h:43:1: error: static_assert failed "int64_t has weird alignment"
MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../mojo/public/c/system/macros.h:15:39: note: expanded from macro 'MOJO_STATIC_ASSERT'
#define MOJO_STATIC_ASSERT(expr, msg) static_assert(expr, msg)
                                      ^             ~~~~
In file included from ../../mojo/core/channel.cc:20:
In file included from ../../mojo/core/core.h:19:
In file included from ../../mojo/core/dispatcher.h:26:
../../mojo/public/c/system/message_pipe.h:38:1: error: static_assert failed "int64_t has weird alignment"
MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../mojo/public/c/system/macros.h:15:39: note: expanded from macro 'MOJO_STATIC_ASSERT'
#define MOJO_STATIC_ASSERT(expr, msg) static_assert(expr, msg)
                                      ^             ~~~~
3 errors generated.

There are more similar errors, and those can be seen at:

http://www.rt-rk.com/mips-buildbot/builders/chromium_build_llvm_latest/builds/75/steps/Build%20Chromium/logs/stdio

Did this work before? N/A 

Chrome version: r603325  Channel: n/a
OS Version: Debian Jessie
Flash Version: Shockwave Flash 31.0 r0

We have a builder which builds Chromium with the latest revision of LLVM. After LLVM rL345419, we started seeing these issues with alignment.
According to https://commondatastorage.googleapis.com/chromium-browser-clang, LLVM 344066 is the last one before change from 345419 is included.