Since pprust is authed impure these can be used for debug logging.

rustc: Make tag_ty_params() and substitute_ty_params() take def ids instead of ty_params, and to check in external crates

Fix error where make check would not produce compilers first, due to make's infinite-recursion-prevention heuristic.

I removed this previously but that was wrong because it caused
block expressions to not create a new scope.

These cases are all dealt with in parse_expr_inner.

This involved making ast.variant spanned.

Still not used, except by the pretty-printer.

The patch also includes a number of smaller fixes to the
pretty-printer that were encountered on the way.

Um, that'd be, align the word *before* retpc. Addresses point to the low part of a word. Un-XFAIL nbody on Darwin.

Ensure task stacks start out with a 16-byte aligned entry frame. Should make OSX behave a bit better.