[clang] [llvm] [Clang] Add __builtin_allow_sanitize_check() (PR #172030)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I guess maybe I'm not sure about the expected usage.  Is the code you're trying to skip over code which performs checks, or code which instruments allocations?  We could potentially have separate builtins which would return different values for those cases.  The documentation doesn't clearly state which case the builtin is intended for.

https://github.com/llvm/llvm-project/pull/172030