PR c/82301 - Updated test case g++.dg/ext/attr-ifunc-1.C (and others) in r253041 segfault on powerpc64

PR c/82301 - Updated test case g++.dg/ext/attr-ifunc-1.C (and others) in r253041 segfault on powerpc64
PR c/82435 - new __attribute__((alias)) warning gets in the way

gcc/ChangeLog:

	PR other/82301
	PR c/82435
	* cgraphunit.c (maybe_diag_incompatible_alias): New function.
	(handle_alias_pairs): Call it.
	* common.opt (-Wattribute-alias): New option.
	* doc/extend.texi (ifunc attribute): Discuss C++ specifics.
	* doc/invoke.texi (-Wattribute-alias): Document.

gcc/testsuite/ChangeLog:

	PR other/82301
	PR c/82435
	* g++.dg/ext/attr-ifunc-1.C: Update.
	* g++.dg/ext/attr-ifunc-2.C: Same.
	* g++.dg/ext/attr-ifunc-3.C: Same.
	* g++.dg/ext/attr-ifunc-4.C: Same.
	* g++.dg/ext/attr-ifunc-5.C: Same.
	* g++.dg/ext/attr-ifunc-6.C: New test.
	* g++.old-deja/g++.abi/vtable2.C: Update.
	* gcc.dg/attr-ifunc-6.c: New test.
	* gcc.dg/attr-ifunc-7.c: New test.
	* gcc.dg/pr81854.c: Update.
	* lib/target-supports.exp: Update.

From-SVN: r253688