[Bug target/120263] RISC-V: FRM not restored if clobbered via inline asm

[vineetg at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120263

--- Comment #3 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
But then makes the case for removing following special case handling

```
static bool
frm_unknown_dynamic_p (rtx_insn *insn)
{
  /* Return true if there is a definition of FRM.  */
  if (reg_set_p (gen_rtx_REG (SImode, FRM_REGNUM), insn))
    return true;

  return false;
}

riscv_frm_mode_after (rtx_insn *insn, int mode)
{
...
  if (frm_unknown_dynamic_p (insn))
    return riscv_vector::FRM_DYN;  <-- this can be MODE_NONE or @ mode itself
```