When deciding whether to convert an array construction loop into a memcpy, look

When deciding whether to convert an array construction loop into a memcpy, look
at whether the *selected* constructor would be trivial rather than considering
whether the array's element type has *any* non-trivial constructors of the
relevant kind.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@167562 91177308-0d34-0410-b5e6-96231b3b80d8