(svn r2688) MSVC and Watcom can't handle identical file names in different directories, oh my...

music/null_m.c

@@ -1,6 +1,6 @@
 #include "stdafx.h"
 #include "openttd.h"
-#include "music/null.h"
+#include "music/null_m.h"
 
 static const char* NullMidiStart(const char* const* parm) { return NULL; }
 static void NullMidiStop(void) {}

music/win32_m.c

@@ -1,6 +1,6 @@
 #include "stdafx.h"
 #include "openttd.h"
-#include "music/win32.h"
+#include "music/win32_m.h"
 #include <windows.h>
 
 static struct {