Fix warnings reported by MSVC

Mainly it's related on a bad practice in SDL to force-define __SSE__
and __SSE2__ flags which generates quite some warnings and causes too
much noise.

There are some other warnings fixed. Should be no functional changes.

NeXyon, please check the changes in audaspace :)

intern/audaspace/SDL/AUD_SDLDevice.h

@@ -32,7 +32,18 @@
 
 #include "AUD_SoftwareDevice.h"
 
+/* SDL force defines __SSE__ and __SSE2__ flags, which generates warnings
+ * because we pass those defines via command line as well. For until there's
+ * proper ifndef added to SDL headers we ignore the redefinition warning.
+ */
+#ifdef _MSC_VER
+#  pragma warning(push)
+#  pragma warning(disable : 4005)
+#endif
 #include <SDL.h>
+#ifdef _MSC_VER
+#  pragma warning(pop)
+#endif
 
 /**
  * This device plays back through SDL, the simple direct media layer.

intern/audaspace/intern/AUD_C-API.cpp

@@ -75,7 +75,6 @@
 #include "AUD_MutexLock.h"
 
 #ifdef WITH_SDL
-#include <SDL.h>
 #include "AUD_SDLDevice.h"
 #endif