PR libstdc++/70437
 	* include/bits/stl_pair.h (_ConstructiblePair,
	_ImplicitlyConvertiblePair, _MoveConstructiblePair,
	_ImplicitlyMoveConvertiblePair): Add shortcut conditions
	for same-type cases.
	* testsuite/20_util/pair/70437.cc: New.

From-SVN: r234743