Linter warning about python version selectors in arch-specific recipes

[jasongrout]

We recently had an issue fixed in jupyterlab-feedstock where we used python version selectors with an arch-specific recipe (i.e., not noarch). This causes problems.

It would be great if the linter warned against using python version selectors in this case, and pointed people to using the skip recipe lines, similar to how the linter warns against using skip in noarch recipes at

conda-smithy/conda_smithy/lint_recipe.py

Lines 270 to 293 in e4b1751

	# 17: noarch doesn't work with selectors
	if build_section.get('noarch') is not None and os.path.exists(meta_fname):
	with io.open(meta_fname, 'rt') as fh:
	in_requirements = False
	for line in fh:
	line_s = line.strip()
	if (line_s == "requirements:"):
	in_requirements = True
	requirements_spacing = line[:-len(line.lstrip())]
	continue
	if line_s.startswith("skip:") and is_selector_line(line):
	lints.append("`noarch` packages can't have selectors. If "
	"the selectors are necessary, please remove "
	"`noarch: {}`.".format(build_section['noarch']))
	break
	if in_requirements:
	if requirements_spacing == line[:-len(line.lstrip())]:
	in_requirements = False
	continue
	if is_selector_line(line):
	lints.append("`noarch` packages can't have selectors. If "
	"the selectors are necessary, please remove "
	"`noarch: {}`.".format(build_section['noarch']))
	break

[jasongrout]

Somewhat related to #528, #257

[djsutherland]

Probably a good thing to add a lint about, but it could be valid if you have python as a build dependency but not host, e.g. a C library that uses a Python build script but doesn't install any Python stuff. Just something to think about in adding the check.