Build from temporary depot (so that relocatability issues are locally reproducible)

[topolarity]

The majority of relocatability issues have to do with reaching into a hard-coded depot or package path on your local machine, and it'd be very nice to be able to detect these problems without a separate machine.

If we use a temporary depot (or a temporarily redirected depot path) during package construction, that path will be gone by the time the user tests the build product locally. That way, relocatability issues referring to your local depot should fail on your local machine.

It's not as good as fixing relocatability at the root causes, but it makes a user a lot less likely to accidentally deliver bad binaries with PackageCompiler.