[clang] [AIX] Turn on `#pragma mc_func` check by default (PR #101336)

[via cfe-commits]

cor3ntin wrote:

Should we consider a feature like `-Wunknown-pragmas=<pragma-name>` rather than doing something specific for that one pragma?
Have you consider whether this use case generalizes at all?


https://github.com/llvm/llvm-project/pull/101336