Compilation fix.

diff --git a/programs/progman/grpfile.c b/programs/progman/grpfile.c
index 01c83de..438c464 100644
--- a/programs/progman/grpfile.c
+++ b/programs/progman/grpfile.c
@@ -6,6 +6,7 @@
  */
 
 #include "windows.h"
+#include "wine/winuser16.h"
 #include "progman.h"
 #include "mmsystem.h"