Refactor dynamic linker, add compartment support

[dbittman]

This PR does a bunch of cleanup and refactoring of the dynamic linker, moving it towards a usable state. It uses that refactoring to implement support for multiple compartments, changing (critically) the dependency search-and-load algorithm to handle multiple compartments with instances of the same underlying library. There are also some changes external to dynlink for supporting some of these new abilities.

This version of the dynamic linker was able to load two libraries into different compartments, each with their own copy of libstd, and execute them. Pretty neat.

Future PRs will:

• Add support for secure gates to the dynamic linker
• Add support for the dynamic linker to indicate the TLS template in a compartment, so that TLS allocation can happen in-compartment.
• Add support for systematic running of constructors and destructors.

One fun thing is that this dynamic linker was written to carefully compartmentalize OS-specific stuff it needs in loading, so in theory, it's portable!

[dbittman]

Also I have no idea why my git config keeps resetting it's like melete is messing with me.

[PandaZ3D]

Do we need a tracking issue for the reference runtime or compartmentalization support?

[dbittman]

Probably, yeah. Although I was planning to play around with the project management stuff, using this as a case-study, soon.