Check for class type before assuming a type is one [PR103703].

Resolves:
PR c++/103703 - ICE with -Wmismatched-tags with friends and templates

gcc/cp/ChangeLog:

	PR c++/103703
	* parser.c (class_decl_loc_t::diag_mismatched_tags): Check for class
	type before assuming a type is one.

gcc/testsuite/ChangeLog:

	PR c++/103703
	* g++.dg/warn/Wmismatched-tags-9.C: New test.