Local repro:

ninja -C out\release obj/third_party/WebKit/Source/core/workers/workers/Precompile-core.cc.obj
ninja: Entering directory `out\release'
[1/1] Regenerating ninja files
[2805/2805] CXX obj/third_party/WebKit/Source/core/workers/workers/Precompile-core.cc.obj
FAILED: obj/third_party/WebKit/Source/core/workers/workers/Precompile-core.cc.obj
../../../../../../src/llvm/build.release/bin/clang-cl.exe /nologo /showIncludes  @obj/third_party/WebKit/Source/core/workers/workers/Precompile-core.cc.obj.rsp /c ../../third_party/WebKit/Source/core/win/Precompile-core.cpp /Foobj/third_party/WebKit/Source/core/workers/workers/Precompile-core.cc.obj /Fd"obj/third_party/WebKit/Source/core/workers/workers_cc.pdb"
Assertion failed: SemaRef.PendingLocalImplicitInstantiations.empty() && "There are local ones at end of translation unit!", file ..\tools\clang\lib\Serialization\ASTWriter.cpp, line 4723
Wrote crash dump file "c:\src\temp\clang-cl.exe-1878a8.dmp"
LLVMSymbolizer: error reading file: PDB Error: Unable to load PDB.  Make sure the file exists and is readable.  Calling loadDataForExe

LLVMSymbolizer: error reading file: PDB Error: Unable to load PDB.  Make sure the file exists and is readable.  Calling loadDataForExe

LLVMSymbolizer: error reading file: PDB Error: Unable to load PDB.  Make sure the file exists and is readable.  Calling loadDataForExe

#0 0x00007ff6b40bd6b5 HandleAbort c:\src\llvm\lib\support\windows\signals.inc:411:0
#1 0x00007ffa92a0dc17 (C:\Windows\System32\ucrtbase.dll+0x6dc17)
#2 0x00007ffa92a0eaa1 (C:\Windows\System32\ucrtbase.dll+0x6eaa1)
#3 0x00007ffa92a10751 (C:\Windows\System32\ucrtbase.dll+0x70751)
#4 0x00007ffa92a10a5f (C:\Windows\System32\ucrtbase.dll+0x70a5f)
#5 0x00007ff6b51fce07 clang::ASTWriter::WriteASTCore(class clang::Sema &,class llvm::StringRef,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class clang::Module *) c:\src\llvm\tools\clang\lib\serialization\astwriter.cpp:4727:0
#6 0x00007ff6b51fc16e clang::ASTWriter::WriteAST(class clang::Sema &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class clang::Module *,class llvm::StringRef,bool) c:\src\llvm\tools\clang\lib\serialization\astwriter.cpp:4596:0
#7 0x00007ff6b51d4a31 clang::PCHGenerator::HandleTranslationUnit(class clang::ASTContext &) c:\src\llvm\tools\clang\lib\serialization\generatepch.cpp:61:0
#8 0x00007ff6b47d49bc clang::MultiplexConsumer::HandleTranslationUnit(class clang::ASTContext &) c:\src\llvm\tools\clang\lib\frontend\multiplexconsumer.cpp:311:0
#9 0x00007ff6b50d3e06 clang::ParseAST(class clang::Sema &,bool,bool) c:\src\llvm\tools\clang\lib\parse\parseast.cpp:171:0
#10 0x00007ff6b47a3130 clang::ASTFrontendAction::ExecuteAction(void) c:\src\llvm\tools\clang\lib\frontend\frontendaction.cpp:1007:0
#11 0x00007ff6b47a2fc7 clang::FrontendAction::Execute(void) c:\src\llvm\tools\clang\lib\frontend\frontendaction.cpp:908:0
#12 0x00007ff6b4765df9 clang::CompilerInstance::ExecuteAction(class clang::FrontendAction &) c:\src\llvm\tools\clang\lib\frontend\compilerinstance.cpp:992:0
#13 0x00007ff6b48261c7 clang::ExecuteCompilerInvocation(class clang::CompilerInstance *) c:\src\llvm\tools\clang\lib\frontendtool\executecompilerinvocation.cpp:255:0
#14 0x00007ff6b2905130 cc1_main(class llvm::ArrayRef<char const *>,char const *,void *) c:\src\llvm\tools\clang\tools\driver\cc1_main.cpp:221:0
#15 0x00007ff6b28ffe74 ExecuteCC1Tool c:\src\llvm\tools\clang\tools\driver\driver.cpp:317:0
#16 0x00007ff6b29021da main c:\src\llvm\tools\clang\tools\driver\driver.cpp:389:0
#17 0x00007ff6b607f9e0 __scrt_common_main_seh f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:283:0
#18 0x00007ffa93768364 (C:\Windows\System32\KERNEL32.DLL+0x8364)
#19 0x00007ffa95c57091 (C:\Windows\SYSTEM32\ntdll.dll+0x67091)
clang-cl.exe: error: clang frontend command failed due to signal (use -v to see invocation)
clang version 7.0.0
Target: i386-pc-windows-msvc
Thread model: posix
InstalledDir: C:\src\llvm\build.release\bin
clang-cl.exe: note: diagnostic msg: PLEASE submit a bug report to http://llvm.org/bugs/ and include the crash backtrace, preprocessed source, and associated run script.
clang-cl.exe: note: diagnostic msg:
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang-cl.exe: note: diagnostic msg: c:\src\temp\Precompile-core-af8941.sh
clang-cl.exe: note: diagnostic msg:

********************
ninja: build stopped: subcommand failed.

Deleted: Precompile-core-af8941.zip 3.1 MB

Precompile-core-af8941.zip 3.1 MB Download

Deleted: Precompile-core-af8941.sh 19.6 KB

Precompile-core-af8941.sh 19.6 KB View Download

Confirmed that it's this one:

---
Author: hans
Date: Tue Feb 13 01:19:43 2018
New Revision: 324991

URL: http://llvm.org/viewvc/llvm-project?rev=324991&view=rev
Log:
Fix for PR32992. Static const classes not exported.

Patch by zahiraam!

Differential Revision: https://reviews.llvm.org/D42968

Modified:
    cfe/trunk/lib/Sema/SemaDeclCXX.cpp
    cfe/trunk/test/CodeGenCXX/dllexport.cpp
---

Reverted in r325133