Do not put incomplete CONSTRUCTORs into static memory

The CONSTRUCTOR_NO_CLEARING flag was invented to avoid generating a memset
for  CONSTRUCTORS that lack elements, but it turns out that the gimplifier
can generate a memcpy for them instead, which is worse performance-wise,
so this prevents it from doing that for them.

	* gimplify.c (gimplify_init_constructor): Do not put the constructor
	into static memory if it is not complete.