xlib_libX11: re-add a patch to fix the keysymdef issue

When xlib_libX11 was bumped to 1.3.2 in commit
1d956c91, the keysymdef patch was
dropped. However, this patch is still needed in order to be able to
tell ./configure where the keysymdef header file is installed.

The patch has been updated for 1.3.2.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>