Although libc++ doesn't yet support Windows we still have Windows builders to track our progress. Currently the clang-cl configuration seems broken because it doesn't support -std=c++11 and instead requires /std:c++11. This patch attempts to fix this. git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@343431 91177308-0d34-0410-b5e6-96231b3b80d8