BUILD: makefile: do not rely on shell substitutions to determine git version

BUILD: makefile: do not rely on shell substitutions to determine git version

Solaris's default shell doesn't support substitutions at the beginning or
end of variables, which are still used to determine the version based on
git. Since we added --abbrev=0 we don't need the last one. And using cut
it's trivial to replace the first one, actually simplifying the whole
expression.

This may be backported to all stable branches.