libgl-gdi: Fix unused-variable warnings.

src/gallium/targets/libgl-gdi/libgl_gdi.c:59:16: warning: ‘use_swr’ defined but not used [-Wunused-variable]
   59 | static boolean use_swr = FALSE;
      |                ^~~~~~~
src/gallium/targets/libgl-gdi/libgl_gdi.c:58:16: warning: ‘use_llvmpipe’ defined but not used [-Wunused-variable]
   58 | static boolean use_llvmpipe = FALSE;
      |                ^~~~~~~~~~~~

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6508>
diff --git a/src/gallium/targets/libgl-gdi/libgl_gdi.c b/src/gallium/targets/libgl-gdi/libgl_gdi.c
index fd7b0ae..59094ec 100644
--- a/src/gallium/targets/libgl-gdi/libgl_gdi.c
+++ b/src/gallium/targets/libgl-gdi/libgl_gdi.c
@@ -55,8 +55,12 @@
 #include "swr/swr_public.h"
 #endif
 
+#ifdef GALLIUM_LLVMPIPE
 static boolean use_llvmpipe = FALSE;
+#endif
+#ifdef GALLIUM_SWR
 static boolean use_swr = FALSE;
+#endif
 
 static struct pipe_screen *
 gdi_screen_create(void)