meson: add subproject fallback for libxcvt

Depends on:
xorg/lib/libxcvt!6

Signed-off-by: Simon Ser <contact@emersion.fr>
4 jobs for cvt-subproject in 2 minutes and 15 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-buster #15544206

00:00:14

 
  Build And Test
passed meson #15544207

00:02:00

passed meson-noglamor #15544208

00:01:52

passed mingw-cross-build #15544209

00:00:41