rust-cpython: fix build for MacOSX MacOSX needs special link flags. Quoting the README of rust-cpython: create a `.cargo/config` with the following content: ``` [target.x86_64-apple-darwin] rustflags = [ "-C", "link-arg=-undefined", "-C", "link-arg=dynamic_lookup", ] ``` This is tested with Python 2.7 (Anaconda install) and Python 3 (Homebrew install)