Summary: Apply patches from the git repo root so paths resolve correctly even when src_dir is a subdirectory of the repo (e.g. fizz, wangle). Without this, patches with paths relative to the repo root fail to apply.

Reviewed By: bigfootjon

Differential Revision: D93644294

fbshipit-source-id: 5e0006eb988eb4cdc6f0ecb0dae8cb35b7189c5d