DeqAsyncHandler: add do ... while (0) to avoid -Wextra-semi-stmt warnings

Clears 12 warnings from clang of the form:

cmsCmap.c:194:34: warning: empty expression statement has no effect;
 remove unnecessary ';' to silence this warning [-Wextra-semi-stmt]
            DeqAsyncHandler(dpy, &async);
                                        ^

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Part-of: <!272>

include/X11/Xlibint.h

@@ -804,12 +804,12 @@ typedef struct _XAsyncEState {
 } _XAsyncErrorState;
 
 extern void _XDeqAsyncHandler(Display *dpy, _XAsyncHandler *handler);
-#define DeqAsyncHandler(dpy,handler) { \
+#define DeqAsyncHandler(dpy,handler) do { \
     if (dpy->async_handlers == (handler)) \
 	dpy->async_handlers = (handler)->next; \
     else \
 	_XDeqAsyncHandler(dpy, handler); \
-    }
+    } while (0)
 
 typedef void (*FreeFuncType) (
     Display*	/* display */