Clear /W3 on MSVC since we use /W4

CMakeLists.txt

@@ -210,6 +210,13 @@ if(MSVC)
         set(C_FLAGS ${C_FLAGS} $<$<COMPILE_LANGUAGE:CXX>:/permissive->)
     endif()
     set(C_FLAGS ${C_FLAGS} /W4 /w14640 /wd4065 /wd4268 /wd4324 /wd5030)
+    # Remove /W3, which is added by default, since we set /W4. Some versions of
+    # MSVC complain about both /W3 and /W4 being specified.
+    foreach(flag_var  CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+        if(${flag_var} MATCHES "-DNDEBUG")
+            string(REGEX REPLACE "/W3" "" ${flag_var} "${${flag_var}}")
+        endif()
+    endforeach()
 
     if(NOT DXSDK_DIR)
         string(REGEX REPLACE "\\\\" "/" DXSDK_DIR "$ENV{DXSDK_DIR}")