Intermediate build step failure, running git across NFS mounts or up in parent non-git directories

> [1233/1233] Generating bin/arducopter_with_bl.hex
> githash md5 a161451f19aabdb06da96d2dbe49a116
> Created bin/arducopter.abin
>
> fatal: not a git repository (or any parent up to mount point /mnt)
> Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
>
> Waf: Leaving directory `/mnt/volume_nyc3_01/custom/base/tmp/copter:CubeOrangePlus:830e2c2fef9c08e7a1faff057b3c207e2253cf84:f9a0f557200efd101ce672f37ffb8e6c/CubeOrangePlus'
>
> BUILD SUMMARY
> Build directory: /mnt/volume_nyc3_01/custom/base/tmp/copter:CubeOrangePlus:830e2c2fef9c08e7a1faff057b3c207e2253cf84:f9a0f557200efd101ce672f37ffb8e6c/CubeOrangePlus

https://custom.ardupilot.org/builds/copter:CubeOrangePlus:830e2c2fef9c08e7a1faff057b3c207e2253cf84:f9a0f557200efd101ce672f37ffb8e6c/

Start with the custom build-server path that invokes Waf for the reported ArduCopter build and reproduce it on the shown NFS-mounted directory. Trace the Git metadata lookup after bin/arducopter.abin is created; done means the build completes without the repository-boundary error outside a Git checkout.

Written by the indexing model from the issue text.