vector::emplace_back was mistakenly requiring move assignable.  Fixed that and did a little drive-by optimization at the same time.  This fixes http://llvm.org/bugs/show_bug.cgi?id=12085.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@151492 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed