[clang] [ClangFE] Improve handling of casting of atomic memory operations. (PR #86691)

[Jonas Paulsson via cfe-commits]

JonPsson1 wrote:

> > I think this case isn't that simple as it is an 80 bit value. Currently that is loaded atomically first with i128, then stored as a temporary and then loaded as an fp80. If I remove that casting, the verifier complains "atomic memory access' operand must have a power-of-two size".
> 
> I think this should be more targeted based on the bitesize. PPCf128 should be simple

Patch updated to handle all FP types except FP80.

https://github.com/llvm/llvm-project/pull/86691