I'm going to break the xcode build

Hello all,

I'd like to submit D32434 soon, which adds a dependency on yaml2obj,
which I use to test elf file parsing code. This will break the xcode
build as it does not provide path to the yaml2obj binary to the unit
tests.

As far as I can tell, fixing the build should be easy and amounts to
adding -DYAML2OBJ=/path/to/yaml2obj to the xcode project config for
compiling unit tests, and you can even do it ahead of time to avoid
breakage.

If there are any issues with this, please let me know sooner rather than later.

cheers,
pavel