[clang] [llvm] Fixes to unblock building LLVM and Clang as Arm64EC (PR #150068)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic approved this pull request.

Not sure if we want to wait on the upstream review in google/benchmark?  Otherwise LGTM.

https://github.com/llvm/llvm-project/pull/150068