[compiler-rt] [compiler-rt] Destroy pthread attrs after use in tests (PR #114923)

[Florian Mayer via llvm-commits]

https://github.com/fmayer commented:

LGTM.

Specifically https://pubs.opengroup.org/onlinepubs/007904875/functions/pthread_create.html:

> If the attributes specified by attr are modified later, the thread's attributes shall not be affected



https://github.com/llvm/llvm-project/pull/114923