AArch64's fctv* instructions implement the saturating behaviour that the
fpto*i.sat intrinsics require, in cases where the destination width
matches the saturation width. Lowering them removes a lot of unnecessary
generated code.
Only scalar lowerings are supported for now.
clang-tidy: warning: invalid case style for function 'LowerFP_TO_INT_SAT' [readability-identifier-naming]
not useful