Fix #54047

(I may have accidentally added it to some auxilliary crates as well;
my emacs-macro-based methodology was pretty crude.)

Implements remaining part of RFC #47.
Addresses issue #16461.

Removed link_attrs from rust.md, they don't appear to be supported by
the parser.

Changed all the tests to use the new extern crate syntax

Change pretty printer to use 'as' syntax

Closes #6738
Closes #7061
Closes #7899
Closes #9719
Closes #10028
Closes #10228
Closes #10401
Closes #11192
Closes #11508
Closes #11529
Closes #11873
Closes #11925

When using tasks in Rust, the expectation is that the runtime does not exit
before all tasks have exited. This is enforced in libgreen through the
`SchedPool` type, and it is enforced in libnative through a `bookkeeping` module
and a global count/mutex pair. Unfortunately, this means that a process which
originates with libgreen will not wait for spawned native tasks.

In order to fix this problem, the bookkeeping module was moved from libnative to
libstd so the runtime itself can wait for native tasks to exit. Green tasks do
not manage themselves through this bookkeeping module, but native tasks will
continue to manage themselves through this module.

Closes #12684

When the timer_helper thread exited, it would attempt to re-acquire the global
task count mutex, but the mutex had previously been deallocated, leading to
undefined behavior of the mutex, and in some cases deadlock.

Another mutex is used to coordinate shutting down the timer helper thread.

Closes #12699

This was previously implemented, and it just needed a snapshot to go through

If the main closure failed, then the `exit_code` variable would still be `None`,
and the `unwrap()` was failing (triggering a process abort). This changes the
`unwrap()` to an `unwrap_or()` in order to prevent process abort and detect when
the native task failed.

If there is a lot of data in thread-local storage some implementations
of pthreads (e.g. glibc) fail if you don't request a stack large enough
-- by adjusting for the minimum size we guarantee that our stacks are
always large enough. Issue #6233.

Closes #7246
Closes #7573

This is required by the check-fast target because each test is slurped up into a
submodule.

 - also removed redundant assignment to is_mutbl
 - updated copyright

Remove disr_val from ast::variant_ and always use ty::variant_info
when the value is needed.  Move what was done during parsing into
other passes, primary typeck.rs.  This move also correctly type checks
the disr. value expression; thus, fixing rustc --pretty=typed when
disr. values are used.