Akin the `py_binary` rules for `lit`, these are scoped to binaries,
rather than exposing the library - binary split. The latter is available
to the package (pip package) users.
Tested:
```
cd utils/bazel
bazel build @llvm-project//llvm:extract_ir
bazel-bin/external/llvm-project/llvm/extract_ir --help
```
...and observed expected output (rather than import not found errors)
(Same for the other 2 targets).
123c83ddc7