[FMV][AIX] Implement target_clones part 2 (target-features) (#206786)
This is part 2 (of 2) of FMV on AIX that would allow specifying
target-feature strings on the ``target_clones`` attribute. Part 1 was in
#177428.
The list of attributes supported is a subset of the attribute accepted
on the `target` attribute on AIX, specifically those that are runtime
detectable via the `__builtin_cpu_supports` builtin.
---------
Co-authored-by: Wael Yehia <wyehia@ca.ibm.com>