c++: loop through array CONSTRUCTOR

c++: loop through array CONSTRUCTOR

I noticed that we were ignoring all the special rules for when to use a
simple INIT_EXPR for array initialization from a CONSTRUCTOR, because
split_nonconstant_init_1 was also passing 1 to the from_array parameter.
Arguably that's the real bug, but I think we can be flexible.

The test that I noticed this with no longer fails without it.

gcc/cp/ChangeLog:

	* init.cc (build_vec_init): Clear from_array for CONSTRUCTOR
	initializer.