meson: Make orcc detectable from other subprojects

If we are a subproject (e.g., gst-build), this can make it possible
to use orcc by other subprojects.
2 jobs for <span class="ref-name">override-program</span> in 1 minute and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #93630
debian sid

00:01:21

failed #93629
debian sid

00:01:40