Other subpackage such as -dev, -doc and even -openrc allow adjusting
depends of the subpackage through such a variable. This is, for
instance, useful to remove a dependency of the origin package from the
-libs subpackage.

While at it document it in APKBUILD(5).

Only run check in fakeroot if options="checkroot" is set. This makes
options="!checkroot" the default.

I expect most checks work as non-root, and if a testsuite requires root,
it will likely fail in fakeroot too. Fakeroot has also shown lower
performance for parallel builds.