mk: Replace 'compile_and_link' with 'oxidize'
auto merge of #12126 : brson/rust/oxidize_mk, r=alexcrichton

I've always thought 'compile_and_link: ...' looked really awkward in our build output. Replace it with something more interesting. I'm open to alternatives to 'oxidize', like 'compile', anything but 'compile_and_link'.
Rearranged enum section of tutorial for clarity.

This version starts with the simple case and builds on it.
auto merge of #12060 : chromatic/rust/enum_tutorial_improvement, r=alexcrichton

This version starts with the simplest case and builds on it. I believe it flows better.