Since we're downloading arbitrary executable code from websites and
running it, we should at least have some confidence it's the right
thing we're running.
Previously a particular package could only ever be installed to target
or native. Instead, allow any package to be installed to either, with
target being the default. Native packages can only ever have native
dependencies, but target packages can depend on native ones in order to
install tools which they need for their build process.
The only place this is needed is when determining the directory name
that the tar file will be extracted to. This can be done by examining
the .tar file name without needing to know the version itself.
These modules encapsulate individual pieces of functionality and make
the code far more maintainable. This is a pretty big refactoring but
overall a big win.
We need to distinguish between tools we compile to use as part of the
build process, and things we build for the eventual target. Install
these into separate install directories; for now, pkg-config is the
only one of these.
