c++: -Wdeprecated-copy and using operator= [PR92145]

c++: -Wdeprecated-copy and using operator= [PR92145]

For the purpose of [depr.impldec] "if the class has a user-declared copy
assignment operator", an operator= brought in from a base class with 'using'
may be a copy-assignment operator, but it isn't a copy-assignment operator
for the derived class.

gcc/cp/ChangeLog:

	PR c++/92145
	* class.c (classtype_has_depr_implicit_copy): Check DECL_CONTEXT
	of operator=.

gcc/testsuite/ChangeLog:

	PR c++/92145
	* g++.dg/cpp0x/depr-copy3.C: New test.