c++: NTTP with array/function type after substitution [PR61355]

We're performing the [temp.param]/10 adjustment at parse time but not
also at substitution time.

	PR c++/61355

gcc/cp/ChangeLog:

	* pt.c (convert_template_argument): Perform array/function to
	pointer conversion on the substituted type of an NTTP.

gcc/testsuite/ChangeLog:

	* g++.old-deja/g++.pt/nontype5.C: Adjust.
	* g++.dg/template/param6.C: New test.