fix name clash on 'GC' between Xlib and Xserver

Both xlib as well as the Xserver use the same identifier "GC" for
different types. While on xlib it's just the numerical ID of a GC,
the xserver defines a struct for it by the same name. This is this
ugly and needs ridiculous hacks for Xserver code that needs xlib.

Easy to solve by just renaming the GC typedef to GCRec (consistent
with how we're naming other structs) and replacing GC* by GCPtr.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

include/gcstruct.h

@@ -279,6 +279,6 @@ typedef struct _GC {
     const GCOps *ops;
     PrivateRec *devPrivates;
     RegionPtr pCompositeClip;
-} GC;
+} GCRec;
 
 #endif                          /* GCSTRUCT_H */