Make more primitive integer methods const

Now that rust-lang#72437 has been merged and `const_if_match` is stable, these methods can be stabilized const. The methods are grouped in commits according to feature names:

* `const_nonzero_int_methods`
    - `NonZero*::new`
* some `const_checked_int_methods`
    - `{i*,u*}::checked_add`
    - `{i*,u*}::checked_sub`
    - `{i*,u*}::checked_mul`
    - `{i*,u*}::checked_neg`
    - `{i*,u*}::checked_shl`
    - `{i*,u*}::checked_shr`
    - `i*::checked_abs`
* `const_saturating_int_methods`
    - `{i*,u*}::saturating_add`
    - `{i*,u*}::saturating_sub`
    - `{i*,u*}::saturating_mul`
    - `i*::saturating_neg`
    - `i*::saturating_abs`
* `const_int_sign`
    - `i*::signum`
* `const_ascii_ctype_on_intrinsics`
    - `{char,u8}::is_ascii_alphabetic`
    - `{char,u8}::is_ascii_uppercase`
    - `{char,u8}::is_ascii_lowercase`
    - `{char,u8}::is_ascii_alphanumeric`
    - `{char,u8}::is_ascii_digit`
    - `{char,u8}::is_ascii_hexdigit`
    - `{char,u8}::is_ascii_punctuation`
    - `{char,u8}::is_ascii_graphic`
    - `{char,u8}::is_ascii_whitespace`
    - `{char,u8}::is_ascii_control`

…arth

Rollup of 4 pull requests

Successful merges:

 - rust-lang#73858 (Make more primitive integer methods const)
 - rust-lang#74487 (Forbid generic parameters in anon consts inside of type defaults)
 - rust-lang#74803 (rustbuild: fix bad usage of UNIX exec() in rustc wrapper)
 - rust-lang#74822 (More ensure stack to avoid segfault with increased `recursion_limit`)

Failed merges:

r? @ghost

- following landing of rust-lang/rust#73858,
the `const_saturing_int_methods` feature is in a weird nonexisting
state (stabilized in a future Rust version), so remove it from the list
to unblock compilation.
- also remove other const features that have stabilized in the
meanwhile to avoid compiler warnings.

- following landing of rust-lang/rust#73858,
the `const_saturing_int_methods` feature is in a weird nonexisting
state (stabilized in a future Rust version), so remove it from the list
to unblock compilation.
- also remove other const features that have stabilized in the
meanwhile to avoid compiler warnings.

The feature `const_saturating_int_methods` used by `staticvec` 0.10.1
has been stabilized by <rust-lang/rust#73858>.

`const_saturating_int_methods` has been stabilized by
<rust-lang/rust#73858>.

Pkgsrc changes:
 * Remove patches now integrated upstream, many related to SunOS / Illumos.
 * The LLVM fix for powerpc is also now integrated upstream.
 * Adapt those patches where the source has moved or parts are integrated.
 * The randomness patches no longer applies, and I could not find
   where those files went...
 * Provide a separate bootstrap for NetBSD/powerpc 9.0, since apparently
   the C++ ABI is different from 8.0.  Yes, this appears to be specific to
   the NetBSD powerpc ports.

Upstream changes:

Version 1.47.0 (2020-10-08)
==========================

Language
--------
- [Closures will now warn when not used.][74869]

Compiler
--------
- [Stabilized the `-C control-flow-guard` codegen option][73893], which enables
  [Control Flow Guard][1.47.0-cfg] for Windows platforms, and is ignored on
  other platforms.
- [Upgraded to LLVM 11.][73526]
- [Added tier 3\* support for the `thumbv4t-none-eabi` target.][74419]
- [Upgrade the FreeBSD toolchain to version 11.4][75204]
- [`RUST_BACKTRACE`'s output is now more compact.][75048]

\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.

Libraries
---------
- [`CStr` now implements `Index<RangeFrom<usize>>`.][74021]
- [Traits in `std`/`core` are now implemented for arrays of any length, not just
  those of length less than 33.][74060]
- [`ops::RangeFull` and `ops::Range` now implement Default.][73197]
- [`panic::Location` now implements `Copy`, `Clone`, `Eq`, `Hash`, `Ord`,
  `PartialEq`, and `PartialOrd`.][73583]

Stabilized APIs
---------------
- [`Ident::new_raw`]
- [`Range::is_empty`]
- [`RangeInclusive::is_empty`]
- [`Result::as_deref`]
- [`Result::as_deref_mut`]
- [`Vec::leak`]
- [`pointer::offset_from`]
- [`f32::TAU`]
- [`f64::TAU`]

The following previously stable APIs have now been made const.

- [The `new` method for all `NonZero` integers.][73858]
- [The `checked_add`,`checked_sub`,`checked_mul`,`checked_neg`, `checked_shl`,
  `checked_shr`, `saturating_add`, `saturating_sub`, and `saturating_mul`
  methods for all integers.][73858]
- [The `checked_abs`, `saturating_abs`, `saturating_neg`, and `signum`  for all
  signed integers.][73858]
- [The `is_ascii_alphabetic`, `is_ascii_uppercase`, `is_ascii_lowercase`,
  `is_ascii_alphanumeric`, `is_ascii_digit`, `is_ascii_hexdigit`,
  `is_ascii_punctuation`, `is_ascii_graphic`, `is_ascii_whitespace`, and
  `is_ascii_control` methods for `char` and `u8`.][73858]

Cargo
-----
- [`build-dependencies` are now built with opt-level 0 by default.][cargo/8500]
  You can override this by setting the following in your `Cargo.toml`.
  ```toml
  [profile.release.build-override]
  opt-level = 3
  ```
- [`cargo-help` will now display man pages for commands rather just the
  `--help` text.][cargo/8456]
- [`cargo-metadata` now emits a `test` field indicating if a target has
  tests enabled.][cargo/8478]
- [`workspace.default-members` now respects `workspace.exclude`.][cargo/8485]
- [`cargo-publish` will now use an alternative registry by default if it's the
  only registry specified in `package.publish`.][cargo/8571]

Misc
----
- [Added a help button beside Rustdoc's searchbar that explains rustdoc's
  type based search.][75366]
- [Added the Ayu theme to rustdoc.][71237]

Compatibility Notes
-------------------
- [Bumped the minimum supported Emscripten version to 1.39.20.][75716]
- [Fixed a regression parsing `{} && false` in tail expressions.][74650]
- [Added changes to how proc-macros are expanded in `macro_rules!` that should
  help to preserve more span information.][73084] These changes may cause
  compiliation errors if your macro was unhygenic or didn't correctly handle
  `Delimiter::None`.
- [Moved support for the CloudABI target to tier 3.][75568]
- [`linux-gnu` targets now require minimum kernel 2.6.32 and glibc 2.11.][74163]

Internal Only
--------
- [Improved default settings for bootstrapping in `x.py`.][73964]
  You can read details about this change in the ["Changes to `x.py`
  defaults"](https://blog.rust-lang.org/inside-rust/2020/08/30/changes-to-x-py-defaults.html)
  post on the Inside Rust blog.

- [Added the `rustc-docs` component.][75560] This allows you to install
  and read the documentation for the compiler internal APIs. (Currently only
  available for `x86_64-unknown-linux-gnu`.)

[1.47.0-cfg]: https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard
[76980]: rust-lang/rust#76980
[75048]: rust-lang/rust#75048
[74163]: rust-lang/rust#74163
[71237]: rust-lang/rust#71237
[74869]: rust-lang/rust#74869
[73858]: rust-lang/rust#73858
[75716]: rust-lang/rust#75716
[75908]: rust-lang/rust#75908
[75516]: rust-lang/rust#75516
[75560]: rust-lang/rust#75560
[75568]: rust-lang/rust#75568
[75366]: rust-lang/rust#75366
[75204]: rust-lang/rust#75204
[74650]: rust-lang/rust#74650
[74419]: rust-lang/rust#74419
[73964]: rust-lang/rust#73964
[74021]: rust-lang/rust#74021
[74060]: rust-lang/rust#74060
[73893]: rust-lang/rust#73893
[73526]: rust-lang/rust#73526
[73583]: rust-lang/rust#73583
[73084]: rust-lang/rust#73084
[73197]: rust-lang/rust#73197
[72488]: rust-lang/rust#72488
[cargo/8456]: rust-lang/cargo#8456
[cargo/8478]: rust-lang/cargo#8478
[cargo/8485]: rust-lang/cargo#8485
[cargo/8500]: rust-lang/cargo#8500
[cargo/8571]: rust-lang/cargo#8571
[`Ident::new_raw`]:  https://doc.rust-lang.org/nightly/proc_macro/struct.Ident.html#method.new_raw
[`Range::is_empty`]: https://doc.rust-lang.org/nightly/std/ops/struct.Range.html#method.is_empty
[`RangeInclusive::is_empty`]: https://doc.rust-lang.org/nightly/std/ops/struct.RangeInclusive.html#method.is_empty
[`Result::as_deref_mut`]: https://doc.rust-lang.org/nightly/std/result/enum.Result.html#method.as_deref_mut
[`Result::as_deref`]: https://doc.rust-lang.org/nightly/std/result/enum.Result.html#method.as_deref
[`TypeId::of`]: https://doc.rust-lang.org/nightly/std/any/struct.TypeId.html#method.of
[`Vec::leak`]: https://doc.rust-lang.org/nightly/std/vec/struct.Vec.html#method.leak
[`f32::TAU`]: https://doc.rust-lang.org/nightly/std/f32/consts/constant.TAU.html
[`f64::TAU`]: https://doc.rust-lang.org/nightly/std/f64/consts/constant.TAU.html
[`pointer::offset_from`]: https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.offset_from