PR c/88546 - Copy attribute unusable for weakrefs

PR c/88546 - Copy attribute unusable for weakrefs

gcc/c-family/ChangeLog:

	PR c/88546
	* c-attribs.c (handle_copy_attribute): Avoid copying attribute leaf.
	Handle C++ empty throw specification and C11 _Noreturn.
	(has_attribute): Also handle C11 _Noreturn.

gcc/ChangeLog:

	PR c/88546
	* attribs.c (decls_mismatched_attributes): Avoid warning for attribute
	leaf.

gcc/testsuite/ChangeLog:

	PR c/88546
	* g++.dg/ext/attr-copy.C: New test.
	* gcc.dg/attr-copy-4.c: Disable macro expansion tracking.
	* gcc.dg/attr-copy-6.c: New test.
	* gcc.dg/attr-copy-7.c: New test.

From-SVN: r267591