Fix -fno-common build failure.

Index: Src/xutils.c
--- Src/xutils.c.orig
+++ Src/xutils.c
@@ -53,6 +53,11 @@ GC		NormalGC;
 XpmIcon		wmgen;
 Pixmap		pixmask;
 
+Display		*display;
+Window		Root;
+Window		iconwin, win;
+int		screen;
+int		DisplayDepth;
 
 /*
  *  Colors for wmCalClock