Index: cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- cmake/modules/HandleLLVMOptions.cmake
+++ cmake/modules/HandleLLVMOptions.cmake
@@ -153,6 +153,12 @@
   endif()
 endfunction()
 
+function(prepend value)
+  foreach(variable ${ARGN})
+    set(${variable} "${value} ${${variable}}" PARENT_SCOPE)
+  endforeach(variable)
+endfunction()
+
 macro(add_flag_if_supported flag name)
   check_c_compiler_flag("-Werror ${flag}" "C_SUPPORTS_${name}")
   append_if("C_SUPPORTS_${name}" "${flag}" CMAKE_C_FLAGS)
@@ -338,7 +344,10 @@
 
   # Enable warnings
   if (LLVM_ENABLE_WARNINGS)
-    append("/W4" msvc_warning_flags)
+    # Put /W4 in front of all the -we flags. cl.exe doesn't care, but for
+    # clang-cl having /W4 after the -we flags will re-enable the warnings
+    # disabled by -we.
+    prepend("/W4" msvc_warning_flags)
     # CMake appends /W3 by default, and having /W3 followed by /W4 will result in 
     # cl : Command line warning D9025 : overriding '/W3' with '/W4'.  Since this is
     # a command line warning and not a compiler warning, it cannot be suppressed except