This uses the pkg-config to find the libgit2 installation on the current development system.
Note: This package still assumes the libgit2 prefix is /usr/local with an absolute include path in the modulemap. Not sure what Swift Package Manager of the 3.1 tools is doing with pkg-config for include paths like it said it would. Right now, it definitely fails to handle just a simple "git2.h" in the modulemap, which the linking seems to work fine with pkg-config.
Can be installed via Homebrew with the following:
$ brew install libgit2Can be installed via APT with the following:
$ sudo apt-get install libgit2