Make get_python_abi more robust/generic

[mbargull]

If a python version that is not listed in

conda-forge-repodata-patches-feedstock/recipe/gen_patch_json.py

Lines 341 to 361 in 13b59ad

	if version.startswith("2.7"):
	if subdir.startswith("linux"):
	return "cp27mu"
	return "cp27m"
	elif version.startswith("2.6"):
	if subdir.startswith("linux"):
	return "cp26mu"
	return "cp26m"
	elif version.startswith("3.4"):
	return "cp34m"
	elif version.startswith("3.5"):
	return "cp35m"
	elif version.startswith("3.6"):
	return "cp36m"
	elif version.startswith("3.7"):
	return "cp37m"
	elif version.startswith("3.8"):
	return "cp38"
	elif version.startswith("3.9"):
	return "cp39"
	return None

is encountered, we get erroneous output, see #90 (comment).
This affects new versions of python and also the existing no-one-ever-uses-python <2.7 packages we have.

[mariusvniekerk]

Since all of our python binaries from 3.9+ are going to just ship with the contraints baked into the package, do we even need to add another (less strict) constraint?

[isuruf]

We should skip adding these for packages built after today by looking at the timestamp