A merge killed while writing hermes_constants.py now reaches the repair (the launcher
imports hermes_bootstrap first), but on a Windows install whose only git is PM's store
copy the repair looked it up through pm, which imports hermes_constants: the lookup
failed, a bare 'git' died with WinError 2 and the tree stayed torn (native mid_git,
run 37198020181). arm_tree_move records the absolute git this run resolved (PATH or
expose_pm_git) and _git_executable prefers it.
(cherry picked from commit 59a744696d3805fdc9fb3f0bf5d5f3b20161cbce)
(cherry picked from commit 8bc8502e336d847a88fc4fd7c408f18d6950377f)
47dcc975ce