-CfAVX girls are still not at ease with frac(single), performance-wise
Now that #38248 was supposedly and mostly fixed, the echoes of past fears linger.
On x64 with `-CfAVX` or `-CfAVX2`, and `-O2` or greater,
```pascal
var
x: single;
begin
x := random;
x := frac(x);
end.
```
compiles into
```nasm
; x := frac(x);
vroundss $0x3,%xmm1,%xmm1,%xmm0
vsubss %xmm0,%xmm1,%xmm0
vcvtss2sd %xmm0,%xmm0,%xmm0
vcvtsd2ss %xmm0,%xmm0,%xmm0
```
Saying straightly, `frac(single)` produces useless single→double→single epilogue.
issue