PR libstdc++/77801
	* include/experimental/numeric: Include <numeric>.
	(__abs): Define.
	(gcd, lcm): Use __abs instead of std::abs.
	* testsuite/experimental/numeric/77801.cc: New test.
	* testsuite/experimental/numeric/gcd.cc: Test unsigned inputs.
	* testsuite/experimental/numeric/lcm.cc: Likewise.

From-SVN: r240656