c++: concepts TS and explicit specialization [PR101098]

c++: concepts TS and explicit specialization [PR101098]

duplicate_decls was not recognizing the explicit specialization as matching
the implicit specialization of g<Y> because
function_requirements_equivalent_p was seeing the C constraint on the
implicit one and not on the explicit.

	PR c++/101098

gcc/cp/ChangeLog:

	* decl.c (function_requirements_equivalent_p): Only compare
	trailing requirements on a specialization.

gcc/testsuite/ChangeLog:

	* g++.dg/concepts/explicit-spec1.C: New test.