[llvm] PPC750cl, and initial support for paired singles (PR #211463)

[Lei Huang via llvm-commits]

https://github.com/lei137 approved this pull request.

Unfortunately most of people on list are not familiar with PPC750cl, thus the lack of responses.  In general this patch looks okay to me with the caveat that I have not looked at the PPC750cl ABI so do not know if the instructions implemented here are correct or not.

https://github.com/llvm/llvm-project/pull/211463