[clang] [ARM] enable FENV_ACCESS pragma support for hard-float targets (PR #137101)

[John Brawn via cfe-commits]

john-brawn-arm wrote:

It's been several years since I looked at this, but from my notes what's needed before setting HasStrictFP=true is:

- Instruction selection patterns for strict fp ops. This is probably just changing e.g. "fadd" to "any_fadd" as I expect for most or all of the instruction selection patterns work fine with strict fp.
- Instructions that can raise fp exceptions need to have mayRaiseFPException=1. Without this transformations can move around or just remove instructions that raise fp exceptions.
- We need proper modelling of reads/write of the FPSCR rounding control bits for controllable rounding modes to be handled correctly.

https://github.com/llvm/llvm-project/pull/137101