Without noshlibprovides in the main package, xbps-src detects every
driver in /usr/lib/sane with an incorrect soname of libsane.so.1 and
adds libsane.so.1 to the shlib-provides list for that package. This
allows ignorepkg=libsane to prevent installation (or allow removal) of
the package that actually installs this shlib, breaking everything that
depends on it. When sane does not provide libsane.so.1, libsane will not
be removable or ignorable when anything depends on the shlib.
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