Fix build with -fno-common

Index: src/wmgeneral/wmgeneral.h
--- src/wmgeneral/wmgeneral.h.orig
+++ src/wmgeneral/wmgeneral.h
@@ -21,7 +21,7 @@ typedef struct {
  /* Global variable */
 /*******************/
 
-Display		*display;
+extern Display		*display;
 
   /***********************/
  /* Function Prototypes */
