[Bug middle-end/50481] builtin to reverse the bit order

[disservin.social at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50481

--- Comment #44 from Disservin <disservin.social at gmail dot com> ---
with avx512bmm on zen6 we could update the reverse to use vbitrevb instead of
relying on gfni https://godbolt.org/z/1fo6jxx45