c++: lambda in non-type template parm type [PR99478]

c++: lambda in non-type template parm type [PR99478]

In this testcase, the non-type template parameter has the type of a
lambda-expression.  This makes no sense because a lambda in template context
is specified to be distinct between different specializations of the
template, even if the lambda is non-dependent, but here which specialization
we are dealing with depends on which lambda we have, and vice versa.

gcc/cp/ChangeLog:

	PR c++/99478
	* parser.c (cp_parser_lambda_expression): Reject lambda
	in template parameter type.

gcc/testsuite/ChangeLog:

	PR c++/99478
	* g++.dg/cpp2a/lambda-uneval14.C: New test.