<bit>: Could has_single_bit() be faster? #5359

Seems like it should convert to popcount(x) == 1 if it's available on the target arch, but looking at the code, doesn't seem like compiler would do it:

_NODISCARD constexpr bool has_single_bit(const _Ty _Val) noexcept {
    return _Val != 0 && (_Val & (_Val - 1)) == 0;
}