Fix Libc++ build with MinGW64

Summary: This patch corrects the build errors I encountered when building on MinGW64.

Reviewers: mati865, rnk, compnerd, smeenai, bcraig

Reviewed By: mati865, smeenai

Subscribers: martell, chapuni, cfe-commits

Differential Revision: https://reviews.llvm.org/D33082

llvm-svn: 304360
diff --git a/libcxx/src/system_error.cpp b/libcxx/src/system_error.cpp
index cbbbb5d..17f2c9a 100644
--- a/libcxx/src/system_error.cpp
+++ b/libcxx/src/system_error.cpp
@@ -65,7 +65,7 @@
 
 string do_strerror_r(int ev);
 
-#if defined(_LIBCPP_MSVCRT)
+#if defined(_LIBCPP_MSVCRT_LIKE)
 string do_strerror_r(int ev) {
   char buffer[strerror_buff_size];
   if (::strerror_s(buffer, strerror_buff_size, ev) == 0)