This failure was spotted in a couple recent builds. The error is the same each time, but the point of failure is different. Here is one example:
JavaScriptCore\DerivedSources\unified-sources\UnifiedSource-bfc896e1-2.cpp(9): fatal error C1090: PDB API call failed, error code '23': (0x000006BA)
[1312/4683] Building CXX object Source\JavaScriptCore\CMakeFiles\JavaScriptCore.dir\__\__\JavaScriptCore\DerivedSources\unified-sources\UnifiedSource-da3fe922-1.cpp.obj
FAILED: Source/JavaScriptCore/CMakeFiles/JavaScriptCore.dir/__/__/JavaScriptCore/DerivedSources/unified-sources/UnifiedSource-da3fe922-1.cpp.obj
I haven't ever seen this in a local build, only in our nightly CI build. Rerunning the build, with no changes, passes.