bp2build: reference static variants directly

Previously, when referencing a cc_library as a static_lib from a
converted module, the corresponding target would depend on the "root
target" of that cc_library. This resulted in a superfluous dependency on
the shared target of the cc_library dependency. This superfluous
dependency could sometimes result in cycles.

This change ensures the static target name is directly specified in such
cases.

Test: mixed_libc.sh CI
Test: USE_BAZEL_ANALYSIS=1 m fmtlib
Change-Id: I36ee9f0a9017b1e9d73df9e3174669107f0afd4f