Packages are either internal packages or external packages. All packages are
considered external packages by default unless explicitly configured as
internal through either the package option LIBFOO_INTERNAL or using
the project configuration
also LIBFOO_EXTERNAL). Both package types are treated the same except
for the following:
An internal package will not generate output warnings if the package is missing licenses.
When configured for local-sources mode, only internal packages which have local sources configured will have their fetch, extract and patch stages skipped.