st/xorg: Silence unused variable warnings.

src/gallium/state_trackers/xorg/xorg_exa.c

@@ -515,6 +515,7 @@ ExaCopy(PixmapPtr pDstPixmap, int srcX, int srcY, int dstX, int dstY,
 #endif
 
    debug_assert(priv == exa->copy.dst);
+   (void) priv;
 
    if (exa->copy.use_surface_copy) {
       /* XXX: consider exposing >1 box in surface_copy interface.

src/gallium/state_trackers/xorg/xorg_exa_tgsi.c

@@ -492,6 +492,7 @@ create_fs(struct pipe_context *pipe,
 
    /* it has to be either a fill, a composite op or a yuv conversion */
    debug_assert((is_fill ^ is_composite) ^ is_yuv);
+   (void) is_yuv;
 
    out = ureg_DECL_output(ureg,
                           TGSI_SEMANTIC_COLOR,

src/gallium/state_trackers/xorg/xorg_renderer.c

@@ -437,6 +437,7 @@ void renderer_copy_prepare(struct xorg_renderer *r,
                                       PIPE_TEXTURE_2D,
                                       PIPE_TEXTURE_USAGE_RENDER_TARGET,
                                       0));
+   (void) screen;
 
 
    /* set misc state we care about */