We were enabling the memcmp optimization in ranges::lexicographical_compare for
signed integral types and for integral types wider than a byte.  But memcmp
gives the wrong answer for arrays of such types.  This patch fixes this issue by
refining the condition that enables the memcmp optimization.  It's now
consistent with the corresponding condition used in
std::lexicographical_compare.

libstdc++-v3/ChangeLog:

	PR libstdc++/93972
	* include/bits/ranges_algo.h (__lexicographical_compare_fn::operator()):
	Fix condition for when to use memcmp, making it consistent with the
	corresponding condition used in std::lexicographical_compare.
	* testsuite/25_algorithms/lexicographical_compare/93972.cc: New test.