Update libgit2 source code (a3ef70b)

* Update libgit2 source code to commit
  a3ef70bb405a05c16fb533d828da2510ff751224

Signed-off-by: Stefan Widgren <stefan.widgren@gmail.com>
Update patch

Signed-off-by: Stefan Widgren <stefan.widgren@gmail.com>
Update Makefile

Signed-off-by: Stefan Widgren <stefan.widgren@gmail.com>