Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -229,9 +229,12 @@
 #  define _LIBCPP_SHORT_WCHAR   1
 // Both MinGW and native MSVC provide a "MSVC"-like enviroment
 #  define _LIBCPP_MSVCRT_LIKE
-// If mingw not explicitly detected, assume using MS C runtime only.
+// If mingw not explicitly detected, assume using MS C runtime only if
+// a MS compatibility version is specified.
 #  ifndef __MINGW32__
-#    define _LIBCPP_MSVCRT // Using Microsoft's C Runtime library
+#    ifdef _MSC_VER
+#      define _LIBCPP_MSVCRT // Using Microsoft's C Runtime library
+#    endif
 #  endif
 #  if (defined(_M_AMD64) || defined(__x86_64__)) || (defined(_M_ARM) || defined(__arm__))
 #    define _LIBCPP_HAS_BITSCAN64