ree needs CFLAGS

fails to build without ... succeeds with

error I got before adding this:
```
/opt/boxen/rbenv/versions/ree-1.8.7-2012.02/lib/ruby/1.8/timeout.rb:60: [BUG] Segmentation fault
ruby 1.8.7 (2012-02-08 MBARI 8/0x6770 on patchlevel 358) [i686-darwin13.2.0], MBARI 0x6770, Ruby Enterprise Edition 2012.02
```
@dgoodlad