Export CMake targets to the build tree

Properly export Vorbis targets when added via `add_subdirectory`.
2 jobs for export-cmake-targets-to-the-build-tree in 1 minute and 45 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed autoconf #10885
docker

00:01:45

passed cmake #10886
docker

00:00:30