librustc: Use separate stack slot for each return.
Reenable ignored test and add run-pass test.
librustc: Add an intrinsic to retrieve the return pointer of a function.

This is needed for some GC stuff in Servo.
librustc: Don't allow return_address intrinsic in functions that don't use an out pointer.
librustc: Don't use Load/Store for structural values.
librustc: Don't use an alloca per return if the function doesn't have nested returns.
libsyntax: Don't strip types and lifetimes from single-segment paths in
patterns.

This breaks code like:

    fn main() {
        match Some("foo") {
            None::<int> => {}
            Some(_) => {}
        }
    }

Change this code to not contain a type error. For example:

    fn main() {
        match Some("foo") {
            None::<&str> => {}
            Some(_) => {}
        }
    }

Closes #16353.

[breaking-change]
auto merge of #16081 : luqmana/rust/nr, r=pcwalton

Fixes #15763
auto merge of #16454 : pcwalton/rust/types-in-path-patterns, r=brson

patterns.

This breaks code like:

    fn main() {
        match Some("foo") {
            None::<int> => {}
            Some(_) => {}
        }
    }

Change this code to not contain a type error. For example:

    fn main() {
        match Some("foo") {
            None::<&str> => {}
            Some(_) => {}
        }
    }

Closes #16353.

[breaking-change]

r? @huonw
Enable deprecation lint on crate-local items

Previously the lint considered cross-crate items only. That's
appropriate for unstable and experimental levels, but not for
deprecation.

Closes #16409

Due to deny(deprecation), this is a:

[breaking-change]
Deprecation fallout in libcollections
Deprecation fallout in libsync
Allow deprecation in deprecated libraries
auto merge of #16433 : aturon/rust/deprecated-in-crate, r=alexcrichton

Previously the stability lint considered cross-crate items only. That's appropriate for unstable and experimental levels, but not for deprecation.

In addition to changing the lint, this PR takes care of the fallout: a number of deprecated items that were being used throughout libstd.

Closes #16409

Due to deny(deprecated), this is a:

[breaking-change]
rustdoc: add tooltips to sidebar