[AArch64] Lowering of fpmode intrinsics in DAG (#80611)
LLVM intrinsics `get_fpmode`, `set_fpmode` and `reset_fpmode` operate
control modes, the bits of FP environment that affect FP operations. On
AArch64 these bits are in FPCR. The lowering implemented to produce code
close to that of GLIBC.
