Solaris support

:construction: 
- [x] Works on 10.11 
- [ ] Works on 10.5
- [ ] Add new entries to $PATH only when the entries are not already present.
- [ ] WIP commits addressed

cc @schisamo @scotthain 
I think we want to avoid this pattern. Wouldn't it be better to export env vars in `Omnibus::Software#with_standard_compiler_flags`. This would match the pattern we used for setting Clang as the default compiler on FreeBSD 10:
https://github.com/opscode/omnibus/blob/master/lib/omnibus/software.rb#L465-L466