Add flag to bypass package dependency resolution

[mizdebsk]

Lets consider implementing a flag for package, which once set would cause dependency resolution to be skipped for given package. Package would be treated as having no build-dependencies - it could never be unresolved, its priority wouldn't be affected by dependencies and so on.

For some packages it may be useful to bypass dependency resolution, for example packages not available on x86_64, or packages with arch-specific BuildRequires.