message: Avoid empty linker_bin_path breaking the build
  If ctx.attr.linker_bin_path is empty (e.g. if should_download_clang is set)
  the GPU build would add a lone `-B` to the build which swallows the next
  argument leading to broken builds.
  Fixes fixes
diff: @@ -500,9 +500,9 @@ def _features(cpu, compiler, ctx):
  flag_groups = [
  flag_group(flags = (
  ["-Wl,-no-as-needed"] if cpu == "local" else []
  - ) + [
  - "-B" + ctx.attr.linker_bin_path,
  - ]),
  + ) + (
  + ["-B" + ctx.attr.linker_bin_path] if ctx.attr.linker_bin_path else []
  + ),
  flag_group(
  flags = ["@%{linker_param_file}"],
  expand_if_available = "linker_param_file",
  