gbuild: Fix and check package dependencies.

Change-Id: Ia54def7a404e07974eb1e8a556f4659cd974e7f8
Reviewed-on: https://gerrit.libreoffice.org/7081
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Matúš Kukan <matus.kukan@collabora.com>