Option to build packages/dependencies from ABS

[ostrich]

Is your feature request related to a problem? Please describe.

This is similar to #5.

My use case is that I am using the unofficial Arch Power distro for IBM POWER processors. This is a small, experimental distro, and its maintainers only provide a subset of packages. However, most packages will compile just fine from the AUR and ABS. This requires manual dependency resolution for any packages not maintained by the distro or not available in the AUR. Such a feature would be very valuable to us niche users.

Describe the solution you'd like

Build package/dependencies from ABS if not available from AUR or official repos. Similar to yaourt's --build option:

SYNC OPTIONS
-b, --build
    Build from sources, ABS for official packages, or AUR if packages is not found. Specify this option twice to build all dependencies.

Describe alternatives you've considered

Build dependencies manually.

Additional context

[idc77]

This option is needed more than ever