2018-05-30  David Pagan  <dave.pagan@oracle.com>

	PR c/55976
	* c-decl.c (grokdeclarator): Update check for return type warnings.
	(start_function): Likewise.
	(finish_function): Likewise.
	* c-typeck.c (c_finish_return): Update check for return type warnings.
	Pass OPT_Wreturn_type to pedwarn when appropriate.

	PR c/55976
	* c-opts.c (c_common_post_options): Set default for warn_return_type
	for C++/C++ with ObjC extensions only. For C, makes it possible to
	differentiate between default (no option), -Wreturn-type, and
	-Wno-return-type.

	PR c/55976
	* gcc.dg/noncompile/pr55976-1.c: New test.
	* gcc.dg/noncompile/pr55976-2.c: New test.

From-SVN: r260978