Fixed header dependencies to be fully compatible with the Windows
headers (with help from Dimitrie O. Paun).

diff --git a/dlls/msacm/msacmdrv.h b/dlls/msacm/msacmdrv.h
index cb8688f..91942e3 100644
--- a/dlls/msacm/msacmdrv.h
+++ b/dlls/msacm/msacmdrv.h
@@ -21,8 +21,13 @@
 #ifndef __WINE_MSACMDRV_H
 #define __WINE_MSACMDRV_H
 
+#include <stdarg.h>
+
 #include "windef.h"
+#include "winbase.h"
 #include "wine/windef16.h"
+#include "mmsystem.h"
+#include "mmreg.h"
 #include "msacm.h"
 
 /***********************************************************************