fix(oss): Resolve a number of build issues only visible in OSS

[ben--]

This PR contains a number of small build fixes -- mostly areas where the OSS EdenFS build had not kept up to date with the internal implementation.

Tested through building Sapling/EdenFS (requires other fixes to run clean):

act --container-architecture linux/x86_64 -W .github/workflows/edenfs_linux.yml

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