libstdc++: Extend std::equal memcmp optimization to std::byte [PR101485]

libstdc++: Extend std::equal memcmp optimization to std::byte [PR101485]

We optimize std::equal to memcmp for integers and pointers, which means
that std::byte comparisons generate bigger code than char comparisons.

We can't use memcmp for arbitrary enum types, because they could have an
overloaded operator== that has custom semantics, but we know that
std::byte doesn't do that.

libstdc++-v3/ChangeLog:

	PR libstdc++/101485
	* include/bits/stl_algobase.h (__equal_aux1): Check for
	std::byte as well.
	* testsuite/25_algorithms/equal/101485.cc: New test.