intrp: Consolidate subproject dep checking and logging

If a dep is not found on the system and a fallback is specified, we
have two cases:

1. Look for the dependency in a pre-initialized subproject
2. Initialize the subproject and look for the dependency

Both these require version comparing, ensuring the fetched variable
is a dependency, and printing a success message, erroring out, etc.

Now we share the relevant code instead of duplicating it. It already
diverged, so this is a good thing.

As a side-effect, we now log fallback dependencies in the same format
as system dependencies:

    Dependency libva found: YES
    Dependency libva found: YES (cached)

    Dependency glib-2.0 from subproject subprojects/glib found: YES
    Dependency glib-2.0 from subproject subprojects/glib found: YES (cached)

0 files changed, 0 insertions, 0 deletions