Please make libsyntax unit tests run?

Per @brson 's request, I'm hoping that he's willing to enable the unit tests associated with libsyntax.  To be absolutely clear, these are the tests that I can run like this:

rustc --test syntax.rc -o syntaxtests && ./syntaxtests

... which appear not to be run currently, as evidenced by the fact that they didn't compile until my recent push.
