PR libstdc++/79162
	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Replace
	with a constrained template.
	[!_GLIBCXX_USE_CXX11_ABI]
	(basic_string<C,T,A>::operator=(basic_string_view<C,T>)): Likewise.
	* testsuite/21_strings/basic_string/cons/char/79162.cc: New test.
	* testsuite/21_strings/basic_string/cons/wchar_t/79162.cc: New test.

From-SVN: r246128