git: disable parallel build for now
git: disable parallel build for now

For some reason, it is unreliable (does not find dependencies even
if they should have been built).

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

dscho/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,git-for-windows/MINGW-packages,git-for-windows/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,git-for-windows/MINGW-packages