In a later change, we would like to generate runtime-deps between
sub-packages.
In order to do that, we can add everything into etc/shlibs or we can
look into other subpackages directly. The former is cumbersome if such
package has lot of shared-objects. The latter requires traversing and
checking a lot of files. Furtunately, we can speed up the latter one by
storing all shared-objects' information in a centralised place.
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