In that case “make config” in “ports/devel/git” directory should present the “flavor” options, among others.
To bypass “config” target to specify just the flavor, see …
Building Packages with poudriere: Initialize Jails and Port Trees,
https://docs.freebsd.org/en/books/handbook/ports/#poudriere-initialization
Flavors tools guide,
https://wiki.freebsd.org/Ports/FlavorsTools