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

The threading library does not recognize AIX and always returns `-1` for
number of physical cores on AIX. This PR teaches the library to
recognize AIX and obtain the correct value for the number of physical

GitOrigin-RevId: 2cac95ba2bd91adb4dad552993d589770ec6996d
3 files changed