Do not propagate dynamic dependencies for stub libs.

Test: m nothing
Test: Build an SDK snapshot including libc, check that the generated
  cc_prebuilt_library_shared for it is a stub that doesn't depend on
  ld-android.
Bug: 152255951
Bug: 154310674
Change-Id: Ie5ec02aebdf00b75756a6eda40db821488d30065