G M:  Restore the ability for libcxx to compile again on mingw 64.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@190837 91177308-0d34-0410-b5e6-96231b3b80d8
Fix typo.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@190857 91177308-0d34-0410-b5e6-96231b3b80d8