Buildbot interrupt can leave directory in an unbuildable state

[huonw]

#7916 failed, and the interrupt managed to catch git mid-operation on mac3, leaving src/llvm such that git doesn't want to run:

fatal: Unable to create '/Users/rustbuild/src/rust-buildbot/slave/auto-mac-all-opt/build/.git/modules/src/llvm/index.lock': File exists.

If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.
Stopping at 'src/llvm'; script returned non-zero status.

(Presumably it's local to the mac3 builder.)

Update: looks like linux3 has also been corrupted:

Synchronizing submodule url for 'src/libuv'
Synchronizing submodule url for 'src/llvm'
configure: git: submodule update
Submodule 'src/libuv' () registered for path 'src/libuv'
Submodule 'src/llvm' () registered for path 'src/llvm'
fatal: Needed a single revision
Unable to find current revision in submodule path 'src/llvm'
configure: error: git

cc @graydon

[graydon]

Sigh, more non-transactional git commands.

I'll try to modify the interrupter to wait until it's done git and configure steps.

[graydon]

I have modified the builder to only interrupt after git and configure. Hopefully this won't happen again. Closing for now. Reopen if you see it happen again.

[sononix]

just download from github and getting this error

[code]
Synchronizing submodule url for 'src/compiler-rt'
Synchronizing submodule url for 'src/gyp'
Synchronizing submodule url for 'src/jemalloc'
Synchronizing submodule url for 'src/libuv'
Synchronizing submodule url for 'src/llvm'
Synchronizing submodule url for 'src/rt/hoedown'
configure: git: submodule init
configure: git: submodule update
fatal: Needed a single revision
Unable to find current revision in submodule path 'src/llvm'
configure: error: git faile
[/code]