c++: Fix list-init of array of no-copy type [PR63707]
build_vec_init_elt models initialization from some arbitrary object of the
type, i.e. copy, but in the case of list-initialization we don't do a copy
from the elements, we initialize them directly.
gcc/cp/ChangeLog:
PR c++/63707
* tree.c (build_vec_init_expr): Don't call build_vec_init_elt
if we got a CONSTRUCTOR.
gcc/testsuite/ChangeLog:
PR c++/63707
* g++.dg/cpp0x/initlist-array13.C: New test.