package/fltk: add optional xlib_libXrender dependency
xlib_libXrender is enabled by default and has been added since version
1.3.4-1 and
https://github.com/fltk/fltk/commit/a6c4b29a184ce7708819f4706877eedcd99a30f5
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 65895f36eea0139c3d590cd5982be5504b2de9ce)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>