c++: array DMI and member fn [PR109666]

c++: array DMI and member fn [PR109666]

Here it turns out I also needed to adjust cfun when stepping out of the
member function to instantiate the DMI.  But instead of adding that tweak,
let's unify with instantiate_body and just push_to_top_level instead of
trying to do the minimum subset of it.  There was no measurable change in
compile time on stdc++.h.

This should also resolve 109506 without yet another tweak.

	PR c++/109666

gcc/cp/ChangeLog:

	* name-lookup.cc (maybe_push_to_top_level)
	(maybe_pop_from_top_level): Split out...
	* pt.cc (instantiate_body): ...from here.
	* init.cc (maybe_instantiate_nsdmi_init): Use them.
	* name-lookup.h: Declare them..

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/nsdmi-array2.C: New test.