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

[Jonas Paulsson via cfe-commits]

JonPsson1 wrote:

> > The non-ieee FP types left out as it seems easier if someone working with that target does this part including test updates, which should be simple enough by now.
> 
> Just add the tests

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". 

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