Unrelated CI failure: "'OMP.inc' has been modified since the precompiled header was built"

[MatzeB]

I am seeing what seems to be unrelated build failures in the CI of my pull request ( #138348 ). Buildkit build https://buildkite.com/llvm-project/github-pull-requests/builds/175644#0196a28c-cb72-4e3e-8b23-be32984cde65

The problematic part seems to be:

FAILED: tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/canonicalize-acc.cpp.o
fatal error: file '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/include/llvm/Frontend/OpenMP/OMP.inc' has been modified since the precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/cmake_pch.hxx.pch' was built: size changed (was 373865, now 373849)
note: please rebuild precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/cmake_pch.hxx.pch'
FAILED: tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/semantics.cpp.o
fatal error: file '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/include/llvm/Frontend/OpenMP/OMP.inc' has been modified since the precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/cmake_pch.hxx.pch' was built: size changed (was 373865, now 373849)
note: please rebuild precompiled header '/var/lib/buildkite-agent/builds/linux-56-59b8f5d88-qkh8m-1/llvm-project/github-pull-requests/build/tools/flang/lib/Semantics/CMakeFiles/FortranSemantics.dir/cmake_pch.hxx.pch'

[boomanaiden154]

Took me a second to realize this was the same as #142449. I'm going to make that one canonical.