When dash is used as the system shell, mod_wsgi fails to build with errors similar to that of apache in
Created attachment 388980 [details]
So I guess the same thing goes here, I guess, that you have to re-emerge apr.
Reinstalling dev-libs/apr-1.5.0-r2 indeed solved the problem. /usr/share/build-1/libtool now explicitely depends on /bin/bash. Maybe apr should be bumped to dev-libs/apr-1.5.0-r3?
See bug 528798
I don't think this is still relevant.