Split out host shared libs target from general-tests

Split out the building of the host shared libs zip from the
general-tests target so it can be built separately. building
general-tests will still build both.

Test: m general-tests, m general-tests-shared-libs
Bug: 314171817
Change-Id: I99f6d7ae5578d8bc97ddc0c047398defbf9b8cc9