[compiler-rt] [compiler-rt] Use installed libc++(abi) for tests instead of build tree (PR #115077)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

Any idea if there is a possibility/risk that this patch introduces some race condition so some files might be used before they're installed?

The reason I'm asking is that we now sometimes see errors like
 compiler-rt/lib/fuzzer/FuzzerExtraCountersWindows.cpp:12:10: fatal error: 'cstdint' file not found

https://github.com/llvm/llvm-project/pull/115077