c++/reflection: ICE with missing OVERLOAD [PR124150]

c++/reflection: ICE with missing OVERLOAD [PR124150]

A function template is supposed to be wrapped in an OVERLOAD.  Since
in certain cases like members_of it is not, splice makes sure to add
the OVERLOAD if needed.  But it wasn't looking into TEMPLATE_ID_EXPRs
and so we ended up with a "naked" TEMPLATE_DECL and crashed.

We can add the missing OVERLOAD in eval_substitute.

	PR c++/124150

gcc/cp/ChangeLog:

	* reflect.cc (eval_substitute): Add an OVERLOAD around
	a DECL_FUNCTION_TEMPLATE_P.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/substitute4.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>