Osx makefile

Hi,

I modified the makefile so that it compiles on Darwin. I've put each change in a separate commit in case you would like to separate them.

The only issue I haven't been able to resolve is the [ArgumentsAdjuster API change](https://github.com/eliben/llvm-clang-samples/issues/10). If you have the time, I would appreciate any input you might have.

Thank you!