Fixes compilation for macOS

[scrogson]

I was unable to get mix compile to work with the git dependencies as the TomlParser doesn't have a clause that matches in proc_value/1.

I saw that it doesn't currently care about much other than getting the name of the project, so I added a catch all clause which allowed compilation to proceed.

I added stderr_to_stdout because the rust compiler was panicing due the way open_port works.

The quotes around the link-args was causing errors, removed those and everything is compiling!

[hansihe]

Thanks!