Add Xcode paths to macos sys_includes

[matthew-levan]

Resolves #26.

[matthew-levan]

When branching this runtime-specific repo off from the urbit monorepo, we initially based off of next/vere in the monorepo. However, during the course of fall 2022, buggy work ended up on next/vere. Because of this, the release branch for version 1.14 of the runtime branched off of master, not next/vere, leading to a non-trivial divergence between next/vere and master. To that end, we have to rewrite the history of this repo, which will potentially obfuscate the commit SHAs and diffs of the already merged PRs in this repo. To provide a trail of breadcrumbs, attached is a patch of the diff represented by this PR before history was rewritten.

PR34.patch