re PR c++/28852 (ICE on invalid conversion operator)

re PR c++/28852 (ICE on invalid conversion operator)

	PR c++/28852
	* cp-tree.h (grok_op_properties): Return bool instead of void.
	* decl.c (grokfndecl): Discard invalid operator declarations.
	(copy_fn_p): Revert change for PR 27547.
	(grok_op_properties): Return error status (true on success).
	* pt.c (tsubst_decl): Discard invalid operator declarations.

	* g++.dg/other/operator1.C: Add error-marker.
	* g++.dg/other/operator2.C: New test.

From-SVN: r116463