Index: libcxx/trunk/cmake/config-ix.cmake
===================================================================
--- libcxx/trunk/cmake/config-ix.cmake
+++ libcxx/trunk/cmake/config-ix.cmake
@@ -50,6 +50,7 @@
                         shell32 user32 kernel32 mingw32 ${MINGW_RUNTIME}
                         moldname mingwex msvcrt)
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_WIN32_WINNT=0x0600")
   endif()
   if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
Index: libcxxabi/trunk/cmake/config-ix.cmake
===================================================================
--- libcxxabi/trunk/cmake/config-ix.cmake
+++ libcxxabi/trunk/cmake/config-ix.cmake
@@ -39,6 +39,7 @@
                         shell32 user32 kernel32 mingw32 ${MINGW_RUNTIME}
                         moldname mingwex msvcrt)
     list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_WIN32_WINNT=0x0600")
   endif()
   if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")