rustc: Append platform exe suffix to output files

Closes #15828
doc: Use vec![] instead of vec!() in Vec.
doc: Fill vec documentation with examples.

Add more useful functions to main example.
doc: Vec::from_raw_parts.

Also more explicit raw pointer handling in unsafe examples.
doc: Normalize example style

Remove unnecessary `use std::vec::Vec`. Use ``` code blocks
with rust as default instead of spelling it out.
clarifying iterator trait documentation
Remove misleading code example from The Guide

The removed code caused confusion because it is not clear that the type of `y` is actually `()`
Clean up some trait impls in core::num.

This removes the special casing for `float`s where it was not necessary, as
`-0.0 == 0.0`.
auto merge of #15869 : alexcrichton/rust/issue-15828, r=kballard

Closes #15828
auto merge of #15894 : treeman/rust/vec-doc, r=alexcrichton

Fill in examples for missing methods. Opt for `vec![]` instead of `vec!()`.
Add Drop support for enums

Fixes #13041.
auto merge of #15272 : jakub-/rust/issue-13041, r=pcwalton

Fixes #13041.
auto merge of #15897 : Gankro/rust/it-docs, r=kballard

I found these things to be ambiguous, or at least worth stating explicitly to reduce the amount a user/developer needs to think about the API.
Remove ancient GC cfg flags
auto merge of #15899 : aochagavia/rust/guide, r=kballard

The removed code caused confusion because it is not clear that the type of `y` is actually `()`
TreeMap examples fixes

1. Removed obsolete comment regarding recursive/iteration implementations of tree_find_with/tree_find_mut_with
2. Replaced easy breakable find_with example with simpler one (which only removes redundant allocation during search)
auto merge of #15900 : tbu-/rust/pr_numcleanup, r=kballard

This removes the special casing for `float`s where it was not necessary, as
`-0.0 == 0.0`.
auto merge of #15910 : sfackler/rust/nogc, r=cmr
auto merge of #15749 : vhbit/rust/treemap-doc-fixes, r=alexcrichton

1. Removed obsolete comment regarding recursive/iteration implementations of tree_find_with/tree_find_mut_with
2. Replaced easy breakable find_with example with simpler one (which only removes redundant allocation during search)
Parser: Global single-segment paths should be represented as PatEnum

Fixed #15774.