VS-Build: Disable /W4 parameter, as it is not picked up anyway

My other PR revealed, that the /W4 parameter, we give to MSVC is ignored
because cmake set CMAKE_C_FLAGS already to /W3 and we overwrite it.

The command line tools gave me a D9025 warning for this on every file and
looking into the project properties page on MSVC 2008 tells, that it has
the warning level set to /W3.

However, the warnings introduced by /W4 are far to useless for having
them enabled. So just disable them.

CMakeLists.txt

@@ -90,7 +90,7 @@ IF (MSVC)
 
     STRING(REPLACE "/Zm1000" " " CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
 
-	SET(CMAKE_C_FLAGS "/W4 /MP /nologo /Zi ${CMAKE_C_FLAGS}")
+	SET(CMAKE_C_FLAGS "/MP /nologo /Zi ${CMAKE_C_FLAGS}")
 	IF (STDCALL)
 	  SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /Gz")
 	ENDIF ()