Automate custom-buiding NUT prerequisites from source

[jimklimov]

Primarily this is needed for easier preparation of WIN32 build environments, compared to building NUT on established Linux/BSD/Solaris/illumos/... distros.

But generally such ability would be useful on many other distributions as well (embedded, alternative approach to packaging, perhaps dockerized, etc.); for example, OmniOS as a minimal server distribution lacks a libusb package.

Some examples of such automation were in https://github.com/zeromq/zproject (which cross-pollinated with NUT about Travis CI support and ci_build.sh for example), and in Makefiles of https://github.com/42ity/FTY dispatcher somewhat modeled after Solaris and OpenIndiana userland maintenance approach.

See also:

• CI: Add a cross-build scenario #1294
• CI: we would benefit from a regular job building against latest third-party code #1333
• Test, script and document linux+mingw builds on non-Debian systems #1472 for Windows build investigation specifically
• Provide more prereqs for linux+mingw builds #1473 for Windows build investigation specifically