Add cc_prebuilt_library helpers for use by the llvm_prebuilt_library_static converter.

Test: bazel build //prebuilts/clang/host/linux-x86:prebuilt_libFuzzer
Test: bazel build //prebuilts/clang/host/linux-x86:prebuilt_libomp
Test: bazel build //prebuilts/clang/host/linux-x86:prebuilt_libunwind
Test: bazel build //prebuilts/clang/host/linux-x86:prebuilt_libunwind-exported

Change-Id: I9343e19a149b62785e8ee3096254776c19675032