[compiler-rt] [Sanitizers] Remove freebsd/netbsd from "posix" file (PR #123269)

[Thurston Dang via llvm-commits]

thurstond wrote:

P.S. Obviously I'd welcome if your patch supports BSD too, but it'd also be acceptable to support only a subset of platforms, and annotate your new test file with something like:
```
// UNSUPPORTED: target={{.*(freebsd|netbsd).*}}
```
or even more restrictively:
```
// REQUIRES: x86_64-linux
```
(to also exclude Mac, Windows, 32-bit Linux, PowerPC, etc.)


https://github.com/llvm/llvm-project/pull/123269