Support relative compile cache

[joyeecheung]

What is the problem this feature will solve?

The built-in compile cache is currently always using absolute paths to decide cache miss/hit, so the cache is not portable.

What is the feature you are proposing to solve the problem?

Support an option for the built-in compile cache to encode the hashes with relative paths and use that to decide cache miss/hit, so that after generating the cache in a specified relative directory, the source directory along with the cache directory can be bundled and moved to elsewhere, and continue to work from a different base directory.

What alternatives have you considered?

No response

[joyeecheung]

@Aditi-1400 has a WIP for this. Since she's not in the organization, assigning this to myself.