Guide: generics
native, rustuv: Fix spawning with empty args

There was a bug in both libnative and libuv which prevented child processes from
being spawned correctly on windows when one of the arguments was an empty
string. The libuv bug has since been fixed upstream, and the libnative bug was
fixed as part of this commit.

When updating libuv, this also includes a fix for #15149.

Closes #15149
Closes #16272
Allow generic foreign functions.

Generic extern functions written in Rust have their names mangled, as well as their internal clownshoe __rust_abi functions. This allows e.g. specific monomorphizations of these functions to be used as callbacks.

Closes #12502.
Add new tests for extern and foreign fns and name mangling.
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
Fix typo in the tutorial
windows: Fix several tests on 64-bit.

Signed-off-by: Peter Atashian <retep998@gmail.com>
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.)
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
Rename `Share` to `Sync`

This leaves the `Share` trait at `std::kinds` via a `#[deprecated]` `pub use`
statement, but the `NoShare` struct is no longer part of `std::kinds::marker`
due to #12660 (the build cannot bootstrap otherwise).

All code referencing the `Share` trait should now reference the `Sync` trait,
and all code referencing the `NoShare` type should now reference the `NoSync`
type. The functionality and meaning of this trait have not changed, only the
naming.

Closes #16281
[breaking-change]
auto merge of #15831 : rpjohnst/rust/generic-foreign-fns, r=alexcrichton

This allows for things like this:

    extern "C" fn callback<T>(t: T) { /* ... */ }
    extern "C" {
        fn take_callback(c: extern fn(i32));
    }

and later:

    take_callback(callback::<i32>);

Closes #12502.
Guide: closures
auto merge of #16317 : adrienbrault/rust/patch-1, r=kballard
Fix typo
Guide: tasks
Guide: strings
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>
Remove spawn-stack-too-big.rs, which is too flaky.