targets/graw-xlib: Add missing dep_x11

targets/graw-xlib: Add missing dep_x11

Required to build Mesa on macOS with

   -Dbuild-tests=true -Dglx=gallium-xlib

Without this change, the build fails with

   In file included from ../src/gallium/targets/graw-xlib/graw_xlib.c:8:
   ../src/gallium/include/frontend/xlibsw_api.h:5:10: fatal error: 'X11/Xlib.h' file not found
   #include <X11/Xlib.h>

With `brew sh` X11 is found but linking fails due to `llvm-ar` missing
in the path. That issue appears to be unrelated to this missing
dependency. X11 is installed via XQuartz, so Homebrew should not be
required.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12022>