signtool: Add bazel build rules Bug: 387241522 Test: ./tools/bazel build @gbl//signtool:gblsigntool Test: bazel-bin/external/gbl/signtool/gblsigntool --help Test: ./tools/bazel run //bootable/libbootloader:gblsigntool_dist Test: out/signtool/gblsigntool --help (cherry picked from https://android-review.googlesource.com/q/commit:16d6fbf4098ddf196e536ded8e48b4699fff78a5) Merged-In: Ie78515ded5a8db0a906c63b9bd42db1ba19efeb7 Change-Id: Ie78515ded5a8db0a906c63b9bd42db1ba19efeb7