c++: assignment from {} with array member NSDMI [PR127016]

can_convert_array only accepts a CONSTRUCTOR or a string literal as a valid
way to aggregate initialize an array.  When the element type needs a loop to
initialize, the digested NSDMI of an array member is a VEC_INIT_EXPR
instead, so we returned false and discarded the implicit assignment
operators as non-viable.  Look through it to VEC_INIT_EXPR_INIT.

	PR c++/127016

gcc/cp/ChangeLog:

	* call.cc (can_convert_array): Handle a VEC_INIT_EXPR FROM.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/initlist-array26.C: New test.

Signed-off-by: Sebastian Miles <sebastianmiles20@gmail.com>