Cleanup collections::slice documentation.

This does a few things:

 - remove references to ~[] and the OwnedVector trait, which are both
   obsolete
 - correct the docs to say that this is the slice module, not the vec
   module
 - add a sentence pointing out that vectors are distinct from Vec
 - remove documentation on Vec.

closes #15459
Guide: tasks
Use system rustc if configured with --enable-local-rust

This commit makes the configuration system autodetect a rustc that
is already installed and use that instead of downloading a snapshot.
fix grammar in Vec.retain's doc comment
Register new snapshot 12e0f72
Fix typo
Guide: method syntax
Guide: strings
windows: Fix several tests on 64-bit.

Signed-off-by: Peter Atashian <retep998@gmail.com>
windows: Fix INVALID_HANDLE_VALUE
Made INVALID_HANDLE_VALUE actually a HANDLE.
Removed all useless casts during INVALID_HANDLE_VALUE comparisons.

Signed-off-by: Peter Atashian <retep998@gmail.com>
make rustdoc more responsive

* move some sidebar contents to a title bar when small
* inline description toggle when small
* make out-of-band and in-band content share space, rather than float and clash
* compress wording of out-of-band content to avoid line-wrap as much as possible
libcollections: Fix RingBuf growth for non-power-of-two capacities
rustc: gensym the module names for --test to avoid introducing user-accessible names.

This requires avoiding `quote_...!` for constructing the parts of the
__test module, since that stringifies and reinterns the idents, losing
the special gensym'd nature of them. (#15962.)
move a test into a run make, to check external affect rather than
implementation details.

(Mainly to avoid accessing the secret internal test module symbol name.)
testsuite: implement #[reexport_test_harness_name] to get access to the
default entrypoint of the --test binary.

This allows one to, e.g., run tests under libgreen by starting it
manually, passing in the test entrypoint.
Move system header includes above valgrind.h include

This allows rustc to be build under msys2's mingw64 gcc
ast_map: Added iterator over all node id's that match a path suffix.

This is useful e.g. for tools need a node-id, such as the flowgraph
pretty printer, since it can avoids the need to first pretty-print the
whole expanded,identified input in order to find out what the node-id
actually is.

It currently only supports path suffixes thst are made up of module
names (e.g. you cannot use the type instantiation form `a::<int>::b`
or `option::Option::unwrap_or` as a path suffix for this tool, though
the tool will produce paths that have non-modulues in the portion of
the path that is not included in the suffix).

(addressed review feedback too)
refactored pprust::State constructor methods out from `pprust::print_crate`.

(Groundwork for pretty-printing only selected items in an input crate.)
Helper method for `pprust::State` for printing instances of `ast_map::Node`.
pretty-printer: let users choose particular items to pretty print.

With this change:

  * `--pretty variant=<node-id>` will print the item associated with
    `<node-id>` (where `<node-id>` is an integer for some node-id in
    the AST, and `variant` means one of {`normal`,`expanded`,...}).

  * `--pretty variant=<path-suffix>` will print all of the items that
    match the `<path-suffix>` (where `<path-suffix>` is a suffix of a
    path, and `variant` again means one of {`normal`,`expanded`,...}).

    Example 1: the suffix `typeck::check::check_struct` matches the
    item with the path `rustc::middle::typeck::check::check_struct`
    when compiling the `rustc` crate.

    Example 2: the suffix `and` matches `core::option::Option::and`
    and `core::result::Result::and` when compiling the `core` crate.

Both of the `--pretty variant=...` modes will include the full path to
the item in a comment that follows the item.

Note that when multiple paths match, then either:

  1. all matching items are printed, in series; this is what happens in
     the usual pretty-print variants, or

  2. the compiler signals an error; this is what happens in flowgraph
     printing.

----

Some drive-by improvements:

Heavily refactored the pretty-printing glue in driver.rs, introducing
a couple local traits to avoid cut-and-pasting very code segments that
differed only in how they accessed the `Session` or the
`ast_map::Map`. (Note the previous code had three similar calls to
`print_crate` which have all been unified in this revision; the
addition of printing individual node-ids exacerbated the situation
beyond tolerance.) We may want to consider promoting some of these
traits, e.g. `SessionCarrier`, for use more generally elsewhere in the
compiler; right now I have to double check how to access the `Session`
depending on what context I am hacking in.

Refactored `PpMode` to make the data directly reflect the fundamental
difference in the categories (in terms of printing source-code with
various annotations, versus printing a control-flow graph).

(also, addressed review feedback.)