Wow, someone has considered my email about freeciv testing good enough
to be put up as wiki page. This is some years old, but for most part
it still applies. New developers (at least) should read it:
It mentions building each client in separate builddir. It's still good
idea to have several builddirs configured for different setups, but
for clients it's nowadays possible to build multiple ones at once with
syntax like '--enable-client=gtk,sdl,xaw,qt'
Freeciv-dev mailing list