devel/git: Update to 2.29.2 and small tweaks

• Update to 2.29.2 [1]
• Simplify logic to define COMMENT for each flavor
• Inspired in www/py-autobahn, save OPTIONS on a different file for each flavor

PR: 250472 [1]
Submitted by: Yasuhiro KIMURA <yasu@utahime.org> [1]
Sponsored by: Rubicon Communications, LLC (Netgate)