[docs] Add note about git version to git-llvm section

[sgraenitz]

Summary

From the mailing list. Git is necessary in one way or other. Version 2.9.3 is 3 years old now and may be a suitable minimum version:
https://git-scm.com/docs/git-remote/2.9.3
What do you think?

[rovka]

Some people might be interested just in compiling LLVM (e.g. fetching some release sources from releases.llvm.org and building them). We should probably keep the package list here focused on that. If we want to add git at all, we should probably mention it somewhere else. I'm not sure where that would be - I suppose somewhere where it makes sense to worry about the minimum version, e.g. where the git-llvm script is concerned. Do we have any other reason to bind ourselves to a certain minimum version of git?

I also notice that the current list mentions make instead of cmake + some build tool of choice. Seems to me we're not very good at keeping our requirements up to date, so maybe we shouldn't add more of them if not super relevant?

[probinson]

See the llvm-commits replies to r365917; at least one code owner is stuck with 1.8.3.

But this should be discussed on llvm-dev first so more people will notice it.

[jyknight]

I don't really want to promise any particular version, because nobody is really checking that particular versions of git work -- the way our scripts continue work with old versions is when developers use them and report a problem. The only real requirement here is "whatever the oldest version someone's actually used recently".

Couple that with git not being a core requirement, I'd rather just say nothing, unless we had an affirmative intent to /not/ support some particular version.

[sgraenitz]

Move git version comment into a footnote in git-llvm section

[sgraenitz]

Remove lldb documentation updates I just added accidentally

[sgraenitz]

Undo Compiling -> Working with

[sgraenitz]

If we want to add git at all, we should probably mention it somewhere else. I'm not sure where that would be - I suppose somewhere where it makes sense to worry about the minimum version, e.g. where the git-llvm script is concerned.

Agree, changed that.

See the llvm-commits replies to r365917; at least one code owner is stuck with 1.8.3.

This is here: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190715/674326.html

The only real requirement here is "whatever the oldest version someone's actually used recently". Couple that with git not being a core requirement, I'd rather just say nothing, unless we had an affirmative intent to /not/ support some particular version.

It may complicate the git-llvm script, but it seems to work so far, so fair enough.

llvm/docs/GettingStarted.rst

 
 .. _commit_from_git:
 
 For developers to commit changes from Git
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 A helper script is provided in ``llvm/utils/git-svn/git-llvm``. After you add it
 to your path, you can push committed changes upstream with ``git llvm
-push``. While this creates a Subversion checkout and patches it under the hood,
-it does not require you to have interaction with it.
+push``\ :sup:`1`. While this creates a Subversion checkout and patches it under
+the hood, it does not require you to have interaction with it.
 
 .. code-block:: console
 
   % export PATH=$PATH:$TOP_LEVEL_DIR/llvm-project/llvm/utils/git-svn/
   % git llvm push
 
 Within a couple minutes after pushing to subversion, the svn commit will have
 been converted back to a Git commit, and made its way into the official Git
 repository. At that point, ``git pull`` should get back the changes as they were
 committed.
 
 You'll likely want to ``git pull --rebase`` to get the official git commit
 downloaded back to your repository. The SVN revision numbers of each commit can
 be found at the end of the commit message, e.g. ``llvm-svn: 350914``.
 
 You may also find the ``-n`` flag useful, like ``git llvm push -n``. This runs
 through all the steps of committing _without_ actually doing the commit, and
 tell you what it would have done. That can be useful if you're unsure whether
 the right thing will happen.
 
+.. note::
+
+   #. The helper script works with git versions >=2.9.3
+
 Reverting a change when using Git
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 If you're using Git and need to revert a patch, Git needs to be supplied a
 commit hash, not an svn revision. To make things easier, you can use
 ``git llvm revert`` to revert with either an SVN revision or a Git hash instead.
 
 Additionally, you can first run with ``git llvm revert -n`` to print which Git