docs: kernel-doc: emit warnings for ancient versions of Python

Kernel-doc requires at least version 3.6 to run, as it uses f-string.
Yet, Kernel build currently calls kernel-doc with -none on some places.
Better not to bail out when older versions are found.

Versions of Python prior to 3.7 do not guarantee to remember the insertion
order of dicts; since kernel-doc depends on that guarantee, running with
such older versions could result in output with reordered sections.

Check Python version when called via command line.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/7d7fa3[e-mail]

scripts/kernel-doc.py

···
 
     logger.addHandler(handler)
 
+    python_ver = sys.version_info[:2]
+    if python_ver < (3,6):
+        logger.warning("Python 3.6 or later is required by kernel-doc")
+
+        # Return 0 here to avoid breaking compilation
+        sys.exit(0)
+
+    if python_ver < (3,7):
+        logger.warning("Python 3.7 or later is required for correct results")
+
     if args.man:
         out_style = ManFormat(modulename=args.modulename)
     elif args.none: