Somehow aligned_union got dropped through the cracks.  This adds it.  Did a drive-by fix of alignment_of while I was in the neighborhood.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@180036 91177308-0d34-0410-b5e6-96231b3b80d8
Modest performance improvement for std::string's operator==.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@180072 91177308-0d34-0410-b5e6-96231b3b80d8
Zero-initialize all mbstate_t in the codecvt tests.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@180108 91177308-0d34-0410-b5e6-96231b3b80d8