[Bug target/110921] Relax _tzcnt_u32 support x86, all x86 arch support for this instrunction

[crazylht at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110921

--- Comment #5 from Hongtao.liu <crazylht at gmail dot com> ---
Maybe source code can be changed as
 int f(int a, int b)
{
    #ifdef __BMI__
        return _tzcnt_u32   (a);
    #else
        return _bit_scan_forward (a);
    #endif
}

But looks like clang/MSVC doesn't support _bit_scan_forward, should be a bug
for them since it's in the intrinsics guide.