Namely, this adds support for:

 * `// dont-check-compiler-stdout`, and
 * `// dont-check-compiler-stderr`.

Obviously almost all ui tests wont want to opt into these, since the whole point
of a ui test is to check the compiler ui. However, since this PR is converting
run-pass into (another set of) ui tests, these header options make sense in that
context.

(Also this puts us into a better position for eventually turning
*every* test suite into a ui test suite, by making ui-ness the default
and forcing tests to opt out explicitly.)

(just like how they behaved under previous run-pass semantics)

This commit fixes a buffer overflow issue in the standard library
discovered by Scott McMurray where if a large number was passed to
`str::repeat` it may cause and out of bounds write to the buffer of a `Vec`.
This bug was accidentally introduced in #48657 when optimizing the
`str::repeat` function. The bug affects stable Rust releases 1.26.0 to
1.29.0. We plan on backporting this fix to create a 1.29.1 release, and
the 1.30.0 release onwards will include this fix.

The fix in this commit is to introduce a deterministic panic in the case of
capacity overflow. When repeating a slice where the resulting length is larger
than the address space, there’s no way it can succeed anyway!

The standard library and surrounding libraries were briefly checked to see if
there were othere instances of preallocating a vector with a calculation that
may overflow. No instances of this bug (out of bounds write due to a calculation
overflow) were found at this time.

Note that this commit is the first steps towards fixing this issue,
we'll be making a formal post to the Rust security list once these
commits have been merged.

constraints:

- clean/inline.rs needs this map to fill in traits when inlining
- fold.rs needs this map to allow passes to fold trait items
- html/render.rs needs this map to seed the Cache.traits map of all
  known traits

The first two are the real problem, since `DocFolder` only operates on
`clean::Crate` but `clean/inline.rs` only sees the `DocContext`. The
introduction of early passes means that these two now exist at the same
time, so they need to share ownership of the map. Even better, the use
of `Crate` in a rustc thread pool means that it needs to be Sync, so it
can't use `Lrc<Lock>` to manually activate thread-safety.

`parking_lot` is reused from elsewhere in the tree to allow use of its
`ReentrantMutex`, as the relevant parts of rustdoc are still
single-threaded and this allows for easier use in that context.

those get handled properly in strip-hidden anyway

This is intended to help solve #54206 on nightly where the RLS on MinGW is
having build issues with accidentally building a `curl` library which links to
pthread symbols on Windows (where it should use native mutex locking instead).
The build system for these `*-sys` crates have all been rewritten to be based on
`cc` to bypass native build systems and platform detection to make sure we
configure them correctly.

The expected.clone() calls were not needed for the tests. This is
just to keep consistency between the test cases.

Let's check out https://github.com/rust-lang/book/pull/1505 on nightly

By introducing a new map that tracks the errors reported and the
`Place`s that spawned those errors against the move out that the error
was referring to, we are able to silence duplicate errors by emitting
only the error which corresponds to the most specific `Place` (that which
other `Place`s which reported errors are prefixes of).

This generally is an improvement, however there is a case -
`liveness-move-in-while` - where the output regresses.

This is useful in debugging when and where errors are emitted in
logs.