git: fix GIT_SKIP_DOCS handling
git: fix GIT_SKIP_DOCS handling

We introduced the option to skip building the documentation (which is
pretty expensive, taking roughly half an hour on this developer's box).

Except it did not work because we built the documentation nevertheless,
just later, in the step that was expected to actually bundle the
documentation... (The reason is that this developer did not quite
understand Bash's array handling idiosynchracies...)

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

git-for-windows/MINGW-packages,vcgato29/MINGW-packages,JanSchulz/MINGW-packages,vcgato29/MINGW-packages,silverkorn/MINGW-packages,JanSchulz/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages,git-for-windows/MINGW-packages,git-for-windows/MINGW-packages,silverkorn/MINGW-packages,dscho/MINGW-packages,vcgato29/MINGW-packages,silverkorn/MINGW-packages,JanSchulz/MINGW-packages,dscho/MINGW-packages,dscho/MINGW-packages