Fix build on Solaris.  The package isn't functional as it looks for gcc
files in hardcoded locations, but perhaps it works on certain releases
anyway, and we can fix the package for SmartOS later.
There was some confusion over the download site; while the software's
homepage links to homepage-relative copies, the announcement e-mail
mentioned the GNU mirror network. This was noticed after reports about
spurious 403 errors came it. Changed to use MASTER_SITES_GNU.
Fix PLIST