[clang] [compiler-rt] [rtsan] Enable RealtimeSanitizer for FreeBSD (PR #125389)

[Allan Jude via llvm-commits]

allanjude wrote:

We have seen interest in all of the different sanitizers from our embedded customers who use FreeBSD to build appliances. We have done work to extend support in FreeBSD for LLVM's KASAN and KMSAN, and have also seen commercial interest in KCSAN and RTSAN

https://github.com/llvm/llvm-project/pull/125389