[compiler-rt] [sanitizer_common][test-only] Specify full path for sort executable in popen.cpp (PR #171622)

[Andrew Haberlandt via llvm-commits]

https://github.com/ndrewh approved this pull request.

I think there's a decent chance this works. I guess maybe the simulator on green dragon runs with a PATH that doesn't have `sort` lol.

https://github.com/llvm/llvm-project/pull/171622