C++: fix-it hint for missing "typename" (PR c++/63392)

C++: fix-it hint for missing "typename" (PR c++/63392)

This patch adds a fix-it hint to missing "typename" errors in the C++
frontend, suggesting the insertion of "typename ".

This addresses part of PR c++/63392; however it does not improve the
error-recovery for such cases.

gcc/cp/ChangeLog:
	PR c++/63392
	* parser.c (cp_parser_diagnose_invalid_type_name): Add fix-it
	hint.

gcc/testsuite/ChangeLog:
	PR c++/63392
	* g++.dg/diagnostic/missing-typename.C: New test.

From-SVN: r263899