Extended Description

Got this error on Firefox CI when trying to build with clang trunk as well as the tip of the release_50 branch (although I'm not 100% sure about the latter, the crash still says clang version 6):

23:25:12 INFO - Wrote crash dump file "C:\Users\task_1501450873\AppData\Local\Temp\clang-cl.exe-5d77f6.dmp"
23:25:12 INFO - #​0 0x0102cce5 llvm::LexicalScopes::getOrCreateLexicalScope(class llvm::DILocalScope const *,class llvm::DILocation const *) (z:\build\build\src\clang\bin\clang-cl.exe+0x4bcce5)
23:25:12 INFO - #​1 0x0102ca0e llvm::LexicalScopes::getMachineBasicBlocks(class llvm::DILocation const *,class llvm::SmallPtrSetImpl<class llvm::MachineBasicBlock const *> &) (z:\build\build\src\clang\bin\clang-cl.exe+0x4bca0e)
23:25:12 INFO - #​2 0x02281259 clang::FriendDecl::anchor(void) (z:\build\build\src\clang\bin\clang-cl.exe+0x1711259)
23:25:12 INFO - #​3 0x00fcd3ea llvm::SparseBitVectorElement<128>::intersectWithComplement(struct llvm::SparseBitVectorElement<128> const &,bool &) (z:\build\build\src\clang\bin\clang-cl.exe+0x45d3ea)
23:25:12 INFO - clang-cl.exe: error: clang frontend command failed due to signal (use -v to see invocation)
23:25:12 INFO - clang version 6.0.0 (trunk 309511)
23:25:12 INFO - Target: i686-pc-windows-msvc
23:25:12 INFO - Thread model: posix
23:25:12 INFO - InstalledDir: z:\build\build\src\clang\bin
23:25:12 INFO - 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.
23:25:12 INFO - clang-cl.exe: note: diagnostic msg:
23:25:12 INFO - ********************
23:25:12 INFO - PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
23:25:12 INFO - Preprocessed source(s) and associated run script(s) are located at:
23:25:12 INFO - clang-cl.exe: note: diagnostic msg: C:\Users\task_1501450873\AppData\Local\Temp\Unified_cpp_layout_style2-74f457.cpp
23:25:12 INFO - clang-cl.exe: note: diagnostic msg: C:\Users\task_1501450873\AppData\Local\Temp\Unified_cpp_layout_style2-74f457.sh
23:25:12 INFO - clang-cl.exe: note: diagnostic msg:
23:25:12 INFO - ********************

I have the two mentioned files and will attach them. I also have the minidump if that helps. For good measure, I'll try a Linux build as well.