Add solaris/amd64 platform to goxc

Added solaris (new in go1.3 http://tip.golang.org/doc/go1.3#solaris) support to goxc. We were able to cross-compile a solaris binary and successfully run it on a solaris machine using this patch. We use goxc for all our cross compilation and it would be awesome if we could get solaris builds out of it as well :)