Newby here, so apologies for any embarassing moments.
(But I’m posting in the spirit of more information being generally better than less.)(Famous last words.)
For me (my platform in subject line) Ardour2 (in the fedora distrib) works
but the current A3 binary segfaults at start, just after getting jack going (A3 always segfaulted in FC15 too).
…But wait…
Building current A3 svn, I get lots of “file not found” errors on the vnum stuff near the end of the build. 
But I can just cp all the offending lib***.so files (and ardour-3.0 itself) over to build/libs/…
and then gtk2_ardour/ardev
works.
With this build I can create and play midi to qsynth, and record and play audio fine.
Storming!
(…Just a strange route to success.)
(I did update a pretty old svn iteration to create this one. Is it possible that something about that is
troubling waf? There are two .waf-***/ directories.)