One calls into C functions passing non-c-like enumerations by
value. The other calls into C expecting non-C-like enumerations as
returns.

These test cases are based on the tests provided by @bitwalker on
issue #68190. The original tests were provided at:
https://github.com/bitwalker/rust_non_c_like_enums_issue/tree/2688d5c672bd4e289085fcdf1c6110e99e7e8ab1

Add a test that demonstrates an incorrect return value when calling into rust with non-c-like-enums.

replace the leak check with universes, take 2

This PR is an attempt to revive the "universe-based region check", which is an important step towards lazy normalization. Unlike before, we also modify the definition of `'empty` so that it is indexed by a universe. This sidesteps some of the surprising effects we saw before -- at the core, we no longer think that `exists<'a> { forall<'b> { 'b: 'a } }` is solveable. The new region lattice looks like this:

```
static ----------+-----...------+       (greatest)
|                |              |
early-bound and  |              |
free regions     |              |
|                |              |
scope regions    |              |
|                |              |
empty(root)   placeholder(U1)   |
|            /                  |
|           /         placeholder(Un)
empty(U1) --         /
|                   /
...                /
|                 /
empty(Un) --------                      (smallest)
```
This PR has three effects:

* It changes a fair number of error messages, I think for the better.
* It fixes a number of bugs. The old algorithm was too conservative and caused us to reject legal subtypings.
* It also causes two regressions (things that used to compile, but now do not).
    * `coherence-subtyping.rs` gets an additional error. This is expected.
    * `issue-57639.rs` regresses as before, for the reasons covered in #57639.

Both of the regressions stem from the same underlying property: without the leak check, the instantaneous "subtype" check is not able to tell whether higher-ranked subtyping will succeed or not. In both cases, we might be able to fix the problem by doing a 'leak-check like change' at some later point (e.g., as part of coherence).

This is a draft PR because:

* I didn't finish ripping out the leak-check completely.
* We might want to consider a crater run before landing this.
* We might want some kind of design meeting to cover the overall strategy.
* I just remembered I never finished 100% integrating this into the canonicalization code.
* I should also review what happens in NLL region checking -- it probably still has a notion of bottom (empty set).

r? @matthewjasper

Rollup of 7 pull requests

Successful merges:

 - #68164 (Selectively disable sanitizer instrumentation)
 - #68413 (Add GitHub issue templates)
 - #68889 (Move the `hir().krate()` method to a query and remove the `Krate` dep node)
 - #68909 (Respect --nocapture in panic=abort test mode)
 - #68910 (Add myself to .mailmap)
 - #68919 (Remove HashStable impl for ast::Lifetime)
 - #68928 (clean up E0276 explanation)

Failed merges:

r? @ghost

clean up E0276 explanation

r? @Dylan-DPC

Remove HashStable impl for ast::Lifetime

Add myself to .mailmap

Respect --nocapture in panic=abort test mode

r? @alexcrichton

Move the `hir().krate()` method to a query and remove the `Krate` dep node

r? @EddyB cc @michaelwoerister

Add GitHub issue templates

This PR adds GitHub's issue templates to the repository. Adding templates for two of the most common issues we create on the repository. We could add more specific templates (e.g. ICEs) depending on the response to initial templates. I've included a screenshot of what it looks like, and people can also try out the UI and specific templates, by going to [`XAMPPRocky/rust`](https://github.com/XAMPPRocky/rust/issues/new/choose).

<img width="1115" alt="Screenshot 2020-01-21 at 13 57 46" src="https://user-images.githubusercontent.com/4464295/72807027-c51baa00-3c56-11ea-8a4c-98238489b345.png">

Selectively disable sanitizer instrumentation

Add `no_sanitize` attribute that allows to opt out from sanitizer
instrumentation in an annotated function.

update miri

Cc @oli-obk r? @ghost

Fixes https://github.com/rust-lang/rust/issues/68878

BtreeMap range_search spruced up

#39457 created a lower level entry point for `range_search` to operate on, but it's really not hard to move it up a level of abstraction, making it somewhat shorter and reusing existing unsafe code (`new_edge` is unsafe although it is currently not tagged as such).

Benchmark added. Comparison says there's no real difference:
```
>cargo benchcmp old3.txt new3.txt --threshold 5
 name                                           old3.txt ns/iter  new3.txt ns/iter  diff ns/iter   diff %  speedup
 btree::map::find_seq_100                       19                21                           2   10.53%   x 0.90
 btree::map::range_excluded_unbounded           3,117             2,838                     -279   -8.95%   x 1.10
 btree::map::range_included_unbounded           1,768             1,871                      103    5.83%   x 0.94
 btree::set::intersection_10k_neg_vs_10k_pos    35                37                           2    5.71%   x 0.95
 btree::set::intersection_staggered_100_vs_10k  2,488             2,314                     -174   -6.99%   x 1.08
 btree::set::is_subset_10k_vs_100               3                 2                           -1  -33.33%   x 1.50
```

r? @Mark-Simulacrum

Rollup of 6 pull requests

Successful merges:

 - #67359 (Rename -Zexternal-macro-backtrace to -Zmacro-backtrace and clean up implementation.)
 - #68524 (Generator Resume Arguments)
 - #68791 (implement proper linkchecker hardening)
 - #68886 (Mark fn map_or() as eagerly evaluated.)
 - #68888 (error code examples: replace some more ignore with compile_fail)
 - #68894 (Update E0565 examples)

Failed merges:

r? @ghost

Update E0565 examples

Fixes #68892

r? @GuillaumeGomez

error code examples: replace some more ignore with compile_fail

Now that #68664 has been merged and `compile_fail` attempts a full build rather than `--emit=metadata`, these errors should be caught by `compile_fail` and do not need to be ignored.

Mark fn map_or() as eagerly evaluated.

In the docs for option.rs and result.rs, it is noted for all *_or()
functions that they are eagerly evaluated, except for the map_or()
function.
This commit adds this missing documentation to the two files.

Closes #68866

implement proper linkchecker hardening

r? @JohnTitor

This implements proper linkcheck filtering... we might need to fiddle with a bit to adjust what is or isn't filtered, but this seems to work reasonable locally.

Generator Resume Arguments

cc https://github.com/rust-lang/rust/issues/43122 and https://github.com/rust-lang/rust/issues/56974

Blockers:
* [x] Fix miscompilation when resume argument is live across a yield point (https://github.com/rust-lang/rust/pull/68524#issuecomment-578459069)
* [x] Fix 10% compile time regression in `await-call-tree` benchmarks (https://github.com/rust-lang/rust/pull/68524#issuecomment-578487162)
  * [x] Fix remaining 1-3% regression (https://github.com/rust-lang/rust/pull/68524#issuecomment-579566255) - resolved (https://github.com/rust-lang/rust/pull/68524#issuecomment-581144901)
* [x] Make dropck rules account for resume arguments (https://github.com/rust-lang/rust/pull/68524#issuecomment-578541137)

Follow-up work:
* Change async/await desugaring to make use of this feature
* Rewrite [`box_region.rs`](https://github.com/rust-lang/rust/blob/3d8778d767f0dde6fe2bc9459f21ead8e124d8cb/src/librustc_data_structures/box_region.rs) to use resume arguments (this shows up in profiles too)

Rename -Zexternal-macro-backtrace to -Zmacro-backtrace and clean up implementation.

This is my attempt at dealing with https://github.com/rust-lang/rust/pull/66364#issuecomment-565517232, although I'm not sure it's the least disruptive one.

The behavior of `-Zexternal-macro-backtrace` was already to enable full macro backtraces for *all* macros, the only part of it that was specific to cross-crate macros was showing this when *not used*:
```
note: this error originates in a macro outside of the current crate
  (in Nightly builds, run with -Z external-macro-backtrace for more info)
```

After this PR:
* the flag is renamed to `-Zmacro-backtrace`
  * do we need to have a deprecation period? cc @rust-lang/compiler
* the message informing you about the flag is always shown when an expansion of a bang macro/attribute/derive is involved, not just cross-crate ones
  * this accounts for most of the changes in tests
  * we could perhaps only show it for the bang macro case? feels odd for derives
* `fix_multispans_in_std_macros` is split into `fix_multispans_in_extern_macros` and `render_multispans_macro_backtrace`
  * this roughly reverts the non-behavioral parts of #46605, which combined the two functionalities
  * not sure where the old `std_macros` name came from, perhaps the `<std macros>` synthetic "file"? even then, odd that `std` specifically was mentioned
* `render_multispan_macro_backtrace`, by default (i.e. without `-Zmacro-backtrace`), hides the `in this macro invocation` label specifically to avoid redundancy in the diagnostic
  * that is, showing the macro use site is only useful when the diagnostic is inside the macro definition and the user can't otherwise tell which use site it applies to, not when the diagnostic is at/inside the use site already (which would make the label redundant)
  * before, it was only checking for the situation in which a cross-crate macro *definition* span would be replaced with the invocation span, which both made the connection to redundancy unobvious, and didn't help with other redundancy (e.g. when the diagnostic was pointing to an argument inside the macro invocation)
  * this accounts for the remaining test changes, which I've first noticed in https://github.com/rust-lang/rust/pull/66364#discussion_r356135967 but only later understood as part of this PR (hence the "redundancy" descriptions)

This PR is not needed for #66364, but it would help, as after this PR there's only one `.span_to_filename(...).is_macros()` check (i.e. for `<... macros>` synthetic "files") left in `rustc_errors`, and it's much more self-contained.

r? @petrochenkov

The intention is that coherence code will skip the leak check and
determine whether two impls *would have* overlapped, and then issue a
warning.

We now make `'empty` indexed by a universe index, resulting
in a region lattice like this:

```
static ----------+-----...------+       (greatest)
|                |              |
early-bound and  |              |
free regions     |              |
|                |              |
scope regions    |              |
|                |              |
empty(root)   placeholder(U1)   |
|            /                  |
|           /         placeholder(Un)
empty(U1) --         /
|                   /
...                /
|                 /
empty(Un) --------                      (smallest)
```

Therefore, `exists<A> { forall<B> { B: A } }` is now unprovable,
because A must be at least Empty(U1) and B is placeholder(U2), and hence
the two regions are unrelated.