dmx: constify GCOps & GCFuncs pointers

Gets rid of 16 instances of gcc 4.8 warnings:

In file included from dmxgc.c:41:0:
dmx.h:327:23: warning: assignment discards ‘const’ qualifier from
 pointer target type [enabled by default]
     (_saved)->_entry  = (_actual)->_entry;    \
                       ^
dmxgc.h:80:5: note: in expansion of macro ‘DMX_WRAP’
     DMX_WRAP(funcs, &dmxGCFuncs, _pGCPriv, (_pGC));   \
     ^
dmxgc.c:192:5: note: in expansion of macro ‘DMX_GC_FUNC_EPILOGUE’
     DMX_GC_FUNC_EPILOGUE(pGC);
     ^

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Reviewed-by: Rémi Cardona <remi@gentoo.org>
Reviewed-by: Keith Packard <keithp@keithp.com>

hw/dmx/dmxgc.c

@@ -49,7 +49,7 @@
 #include "pixmapstr.h"
 #include "migc.h"
 
-static GCFuncs dmxGCFuncs = {
+static const GCFuncs dmxGCFuncs = {
     dmxValidateGC,
     dmxChangeGC,
     dmxCopyGC,
@@ -59,7 +59,7 @@ static GCFuncs dmxGCFuncs = {
     dmxCopyClip,
 };
 
-static GCOps dmxGCOps = {
+static const GCOps dmxGCOps = {
     dmxFillSpans,
     dmxSetSpans,
     dmxPutImage,

hw/dmx/dmxgc.h

@@ -41,8 +41,8 @@
 
 /** GC private area. */
 typedef struct _dmxGCPriv {
-    GCOps *ops;
-    GCFuncs *funcs;
+    const GCOps *ops;
+    const GCFuncs *funcs;
     XlibGC gc;
     Bool msc;
 } dmxGCPrivRec, *dmxGCPrivPtr;