add the osx validation in in GIT_VERSION global variable

[elzerver]

There was an error when awk tries to get the substring from git version.

[javier-lopez]

Hello Aldo,

While I ack the issue I'm afraid I won't be able to merge this PR as it is, if you are willing to work though it I'll require than you avoid leaving commented code, only use posix valid code, eg, no [[ usage, you can test your changes with https://www.shellcheck.net/ to verify you're not using bashisms, last but not least, the code should be as generic as possible, for this specific case I think you could grab the GIT_VERSION logic into a _git_version function or something similar, also please avoid leaving TODO if / else statements, we can always add them as other users complain about their specific platform.