Disable -Wreturn-type by default in all languages other from C++.

Disable -Wreturn-type by default in all languages other from C++.

2017-11-15  Martin Liska  <mliska@suse.cz>

	* tree-cfg.c (pass_warn_function_return::execute):
	Compare warn_return_type for greater than zero.
2017-11-15  Martin Liska  <mliska@suse.cz>

	* options.c (gfc_post_options):
	Do not set default value of warn_return_type.
	* trans-decl.c (gfc_trans_deferred_vars):
	Compare warn_return_type for greater than zero.
	(generate_local_decl): Likewise
	(gfc_generate_function_code): Likewise.

From-SVN: r254764