git: Wire up Git v2.39 execution environment
Wire up the Git v2.39 execution environment so that we can toggle between the v2.38 and v2.39 release tracks. Major new features that we're interested in include:
- The upstreamed patch to improve git-receive-pack(1)'s connectivity
check to not use all local refs as boundary anymore. This is a
performance improvement that we have already backported into Git
v2.38.2.gl1.
- git-merge-tree(1) has learned a new `--stdin` flag to perform a
series of merges. This may prove useful to to iterate on our
migration away from libgit2.
- git-repack(1) has learned to delete packfile bitmaps when writing
multi-pack-index bitmaps.
- A deadlock in git-repack(1) when receiving a signal, which we have
also hit in production systems.
- A fix where git-patch-id(1) didn't account for changed binary
files.
There are naturally various other new features, bugfixes and performance improvements.
The new Git v2.39 binary is protected by a feature flag.
Edited by Patrick Steinhardt