Makefile: Adapt to changed build options in libgit2 v1.5.0
This MR adapts to changed build options in libgit2 v1.5.0 and newer. Most importantly this fixes how we disable building tests, which right now causes us to pull in Python.
This MR adapts to changed build options in libgit2 v1.5.0 and newer. Most importantly this fixes how we disable building tests, which right now causes us to pull in Python.