[llvm] [AIX][PowerPC] Teach the Threading Library About the Number of Physical Cores on AIX (PR #67683)

[Qiongsi Wu via llvm-commits]

qiongsiwu wrote:

@xingxue-ibm Thanks for the suggested changes. The PR is revised. Could you take a look? Thanks so much! 

https://github.com/llvm/llvm-project/pull/67683