[llvm] Change `fp128` lowering to use `f128` functions by default (PR #76558)

[Trevor Gross via llvm-commits]

tgross35 wrote:

@arsenm would you mind taking a look at this? It should fix most of the problems with unsoundly lowering f128 to long double calls. No control via target string, I'll do that separately.

Does https://github.com/llvm/llvm-project/blob/50aacb9e1b51811f12cb017719678962411c50dd/llvm/lib/CodeGen/IntrinsicLowering.cpp#L386-L445 need to be updated somehow?

https://github.com/llvm/llvm-project/pull/76558