The printing of the error message on stack overflow had two sometimes false
assumptions previously. The first is that a local task was always available (it
called Local::take) and the second is that it used `println!` instead of
manually writing.

The first assumption isn't necessarily true because while stack overflow will
likely only be detected in situations that a local task is available, it's not
guaranteed to always be in TLS. For example, during a `println!` call a task
may be blocking, causing it to be unavailable. By using Local::try_take(), we
can be resilient against these occurrences.

The second assumption could lead to odd behavior because the stdout logger can
be overwritten to run arbitrary code. Currently this should be possible, but the
utility is much diminished because a stack overflow translates to an abort()
instead of a failure.

…=Veykril

Introduce macro sub-namespaces and `macro_use` prelude

This PR implements two mechanisms needed for correct macro name resolution: macro sub-namespace and `macro_use` prelude.

- [macro sub-namespaces][subns-ref]

  Macros have two sub-namespaces: one for function-like macro and the other for those in attributes (including custom derive macros). When we're resolving a macro name for function-like macro, we should ignore non-function-like macros, and vice versa.

  This helps resolve single-segment macro names because we can (and should, as rustc does) fallback to names in preludes when the name in the current module scope is in different sub-namespace.

- [`macro_use` prelude][prelude-ref]

  `#[macro_use]`'d extern crate declarations (including the standard library) bring their macros into scope, but they should not be prioritized over local macros (those defined in place and those explicitly imported).

  We have been bringing them into legacy (textual) macro scope, which has the highest precedence in name resolution. This PR introduces the `macro_use` prelude in crate-level `DefMap`s, whose precedence is lower than local macros but higher than the standard library prelude.

The first 3 commits are drive-by fixes/refactors.

Fixes rust-lang#8828 (prelude)
Fixes rust-lang#12505 (prelude)
Fixes rust-lang#12734 (prelude)
Fixes rust-lang#13683 (prelude)
Fixes rust-lang#13821 (prelude)
Fixes rust-lang#13974 (prelude)
Fixes rust-lang#14254 (namespace)

[subns-ref]: https://doc.rust-lang.org/reference/names/namespaces.html#sub-namespaces
[prelude-ref]: https://doc.rust-lang.org/reference/names/preludes.html#macro_use-prelude

`manual_assert`: do not add extra semicolon

Fixes rust-lang#12505

changelog: [`manual_assert`]: do not add extra semicolon to suggestion