CodeGen, Driver: Introduce -fpreferred-function-alignment option.
This option may be used to specify a function's preferred alignment.
The -falign-functions option and the aligned attribute now control
both the minimum alignment and the preferred alignment for consistency
with gcc. In contrast to the previous approach implemented in #149444
the preferred alignment is retained for member functions.
Part of this RFC:
https://discourse.llvm.org/t/rfc-enhancing-function-alignment-attributes/88019
Reviewers: vitalybuka, MaskRay, AaronBallman, jansvoboda11
Pull Request: https://github.com/llvm/llvm-project/pull/155528