Log Message:
p5-Alien-Build: fix build support for SunOS + pkgconf

Don't assume pkgconf won't work on Solaris derivates and disallow its
use. (This package being a tool that's used by other packages for
builds.) Addresses a failure of p5-Alien-Hunspell to build on SunOS
only. (Which in turn is required for p5-Text-Hunspell these days.)