Build fixes for Tiger

Both bison and python on Tiger are too old to build doxygen, so brew newer ones
In that case, specify:

```rb
fails_with :gcc do
  build 5553 # or whatever the build number of Tiger's GCC is
  cause "Snippet of the build output, or other explanation of the build failure"
end
```

That will automatically trigger a fallback to another compatible compiler, which might be GCC 4.0 or a newer FSF GCC, depending on what the user has installed.