[PowerPC][AIX] Support ByVals with greater alignment then pointer size (#93341)

Implementation is NOT compatible with IBM XL C 16.1 and earlier but is
compatible with GCC.
It handles all ByVals with greater alignment then pointer width the same
way IBM XL C handles Byvals
that have vector members. For overaligned objects that do not contain
vectors IBM XL C does not align them properly if they are passed in the
GPR
argument registers.

This patch was originally written by Sean Fertile @mandlebug. 

Previously on Phabricator https://reviews.llvm.org/D105659