For example from https://build.chromium.org/p/chromium.fyi/builders/ClangToTWin/builds/13012:

FAILED: bin/c-index-test.exe 
cmd.exe /C "cd . && C:\b\c\builder\ClangToTWin\src\third_party\llvm-build-tools\cmake-3.4.3-win32-x86\bin\cmake.exe -E vs_link_exe --intdir=tools\clang\tools\c-index-test\CMakeFiles\c-index-test.dir --manifests  -- C:\b\c\win_toolchain\vs_files\f53e4598951162bad6330f7a167486c7ae5db1e5\VC\bin\amd64\link.exe /nologo tools\clang\tools\c-index-test\CMakeFiles\c-index-test.dir\c-index-test.c.obj tools\clang\tools\c-index-test\CMakeFiles\c-index-test.dir\core_main.cpp.obj tools\clang\tools\c-index-test\CMakeFiles\c-index-test.dir\__\__\__\__\resources\windows_version_resource.rc.res  /out:bin\c-index-test.exe /implib:lib\c-index-test.lib /pdb:bin\c-index-test.pdb /version:0.0  /DEBUG /OPT:REF /OPT:ICF /STACK:10000000 /INCREMENTAL:NO /subsystem:console  lib\LLVMSupport.lib lib\libclang.lib lib\clangAST.lib lib\clangBasic.lib lib\clangCodeGen.lib lib\clangFrontend.lib lib\clangIndex.lib lib\clangSerialization.lib lib\LLVMCoroutines.lib lib\LLVMCoverage.lib lib\LLVMLTO.lib lib\LLVMObjCARCOpts.lib lib\LLVMPasses.lib lib\LLVMipo.lib lib\LLVMIRReader.lib lib\LLVMAsmParser.lib lib\LLVMLinker.lib lib\LLVMInstrumentation.lib lib\LLVMVectorize.lib lib\LLVMCodeGen.lib lib\LLVMBitWriter.lib lib\LLVMScalarOpts.lib lib\LLVMInstCombine.lib lib\LLVMTarget.lib lib\LLVMTransformUtils.lib lib\LLVMAnalysis.lib lib\LLVMObject.lib lib\clangFrontend.lib lib\LLVMProfileData.lib lib\clangDriver.lib version.lib lib\clangParse.lib lib\LLVMMCParser.lib lib\LLVMOption.lib lib\clangSerialization.lib lib\LLVMBitReader.lib lib\clangSema.lib lib\clangAnalysis.lib lib\clangEdit.lib lib\clangFormat.lib lib\clangToolingCore.lib lib\clangAST.lib lib\clangRewrite.lib lib\clangLex.lib lib\clangBasic.lib lib\LLVMCore.lib lib\LLVMBinaryFormat.lib lib\LLVMMC.lib lib\LLVMSupport.lib psapi.lib shell32.lib ole32.lib uuid.lib lib\LLVMDemangle.lib kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib && cd ."
LINK : fatal error LNK1285: corrupt PDB file 'C:\b\c\builder\ClangToTWin\src\third_party\llvm-build\Release+Asserts\bin\c-index-test.pdb'; delete and rebuild
LINK failed. with 1285

Looks like it's just that one bot, though.