c++: dependent generic lambda template-id [PR106024]

c++: dependent generic lambda template-id [PR106024]

We were wrongly looking up the generic lambda op() in a dependent scope, and
then trying to look up its instantiation at substitution time, but lambdas
aren't instantiated, so we crashed.  The fix is to not look into dependent
class scopes.

But this created trouble with wrongly trying to use a template from the
enclosing scope when we aren't actually looking at a template-argument-list,
in template/lookup18.C, so let's avoid that.

	PR c++/106024

gcc/cp/ChangeLog:

	* parser.cc (missing_template_diag): Factor out...
	(cp_parser_id_expression): ...from here.
	(cp_parser_lookup_name): Don't look in dependent object_type.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/lambda-generic10.C: New test.