[libc] Inherit integration test dependencies from the startup target

All integration tests rely on the startup code to be run. Currently we
manually include a few of these dependencies that are relevant for the
Linux target. This patch changes this to make the integration test's
dependencies include all the dependencies of the startup code. This
simplifies the code and makes it easier to support different targets.
The changes here cause the integration test to be dependent on more
targets than previously necessary, but it should be fine.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D146184