Fix build with -fno-common

Index: wmgeneral/wmgeneral.h
--- wmgeneral/wmgeneral.h.orig
+++ wmgeneral/wmgeneral.h
@@ -36,7 +36,7 @@ typedef struct {
  /* Global variable */
 /*******************/
 
-Display		*display;
+extern Display		*display;
 
   /***********************/
  /* Function Prototypes */