Add Perl module in compartment 3

[endbr64]

This runs both RTMP and Perl modules in Nginx. Test Perl by running curl localhost:8080/perl.

TODO:

• figure out why the rewriter exits with an error
• ensure this is actually working

[ayrtonm]

IIRC our build process currently doesn't support more than two compartments. The issue is that call gate wrappers for direct calls are named __wrap_$FN_NAME, but they are specific to a pair of pkeys (caller/target). In the case where the main binary provides a function foo which both modules need to call, we'll need a call gate wrapper for each compartment for foo. Basically something like __wrap_foo_from_2 and __wrap_foo_from_3 (the target pkey is implicit since foo is defined in compartment 1).

I think we can make this work with something like objcopy --redefine-sym foo=foo_from_1 as explained in the 'Define call gates for direct transitions' section of #174, but we'll have to reread that to make sure it works. I believe there is not an analogous problem with the names of indirect call gate wrappers, but it'd be worth double checking.

[ayrtonm]

See #276 for list of blockers

[rinon]

Closing this, as I don't think we have plans to land it. We can always re-open if it becomes relevant.