[compiler-rt] [compiler-rt] fix/check __sanitizer_siginfo type on apple. (PR #77464)

[Miod Vallat via llvm-commits]

dustanddreams wrote:

FWIW, the discrepancy was also mentioned in #63824 with a possible fix which also fixes the definition of `ucontext_t`, which fell on deaf ears.

https://github.com/llvm/llvm-project/pull/77464