Improve lifetime errors with implicit trait object lifetimes

[mark-i-m]

r? @matthewjasper

cc @estebank

I still think the ideal solution would be to construct a BrAnon, but that seems like a more invasive change, and can be done later. This at least gets rid of the hack in OutliveSuggestion and is slightly more principled.

[matthewjasper]

This appears to apply to more than just trait objects.
r=me with comments addressed.

[matthewjasper]

@bors r+

[bors]

📌 Commit 8f4d3632b03d8526f643c9ccab99172f02a83a07 has been approved by matthewjasper

[bors]

☔ The latest upstream changes (presumably #66824) made this pull request unmergeable. Please resolve the merge conflicts.

[mark-i-m]

Rebased, but need to rerun tests and bless...

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-28T01:33:03.3582393Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-28T01:33:03.3766918Z ##[command]git config gc.auto 0
2019-11-28T01:33:03.3852344Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-28T01:33:03.3906386Z ##[command]git config --get-all http.proxy
2019-11-28T01:33:03.4053497Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66679/merge:refs/remotes/pull/66679/merge
---
2019-11-28T01:46:46.2614698Z    Compiling syntax_expand v0.0.0 (/checkout/src/libsyntax_expand)
2019-11-28T01:47:50.1012421Z    Compiling rustc_typeck v0.0.0 (/checkout/src/librustc_typeck)
2019-11-28T01:51:25.1719098Z    Compiling rustc_lint v0.0.0 (/checkout/src/librustc_lint)
2019-11-28T01:52:02.3444682Z    Compiling rustc_mir v0.0.0 (/checkout/src/librustc_mir)
2019-11-28T01:52:06.5009920Z error[E0599]: no method named `synthesize_region_name` found for type `&borrow_check::nll::region_infer::RegionInferenceContext<'tcx>` in the current scope
2019-11-28T01:52:06.5013859Z     |
2019-11-28T01:52:06.5013859Z     |
2019-11-28T01:52:06.5014213Z 312 |                         let name = self.synthesize_region_name(renctx);
2019-11-28T01:52:06.5014779Z     |                                         ^^^^^^^^^^^^^^^^^^^^^^ method not found in `&borrow_check::nll::region_infer::RegionInferenceContext<'tcx>`
2019-11-28T01:52:12.4188321Z error: aborting due to previous error
2019-11-28T01:52:12.4188422Z 
2019-11-28T01:52:12.4189015Z For more information about this error, try `rustc --explain E0599`.
2019-11-28T01:52:12.5010823Z error: could not compile `rustc_mir`.
---
2019-11-28T01:54:06.5159482Z   local time: Thu Nov 28 01:54:06 UTC 2019
2019-11-28T01:54:06.8158913Z   network time: Thu, 28 Nov 2019 01:54:06 GMT
2019-11-28T01:54:06.8160071Z == end clock drift check ==
2019-11-28T01:54:09.6815800Z 
2019-11-28T01:54:09.6914662Z ##[error]Bash exited with code '1'.
2019-11-28T01:54:09.6945626Z ##[section]Starting: Checkout
2019-11-28T01:54:09.6947350Z ==============================================================================
2019-11-28T01:54:09.6947421Z Task         : Get sources
2019-11-28T01:54:09.6947467Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[mark-i-m]

@matthewjasper I think this is ready now :)

[matthewjasper]

@bors r+

[bors]

📌 Commit 2a86b6c has been approved by matthewjasper

[bors]

🌲 The tree is currently closed for pull requests below priority 1000, this pull request will be tested once the tree is reopened