LAKITU: add functionality required for PEP517 code in distutils eclass

- allow pythonN.M format in the impl compat lines
- Allow python_domodule run in phases other than install if
    BUILD_DIR is set

BUG=b/257113269
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I360fe7de88cf6c8888de5ae385a9b4ff110169cd
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/eclass-overlay/+/42429
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Vaibhav Rustagi <vaibhavrustagi@google.com>