Custom backtrace output for Fuchsia

[cramertj]

This is... not my favorite code that I've ever written. This lovely platform-agnostic module is no longer platform-agnostic. I considered breaking it up more, but the public API for other crates has to remain roughly the same in order to fulfill their needs on other platforms, and the actual quantity of cfg'd code here is fairly small-- it seems wrong to introduce a non-sys-common sys/fuchsia/backtrace.rs and sys/everything_but_fuchsia/backtrace.rs. Let me know if you have better suggestions for organizing this.

r? @alexcrichton

[rust-highfive]

The job mingw-check of your PR failed (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.

2019-09-03T21:02:29.6897354Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-09-03T21:02:29.7093142Z ##[command]git config gc.auto 0
2019-09-03T21:02:29.7167218Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-09-03T21:02:29.7215054Z ##[command]git config --get-all http.proxy
2019-09-03T21:02:29.7345903Z ##[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/64133/merge:refs/remotes/pull/64133/merge
---
2019-09-03T21:06:20.5028415Z ##                                                                         3.3%
2019-09-03T21:06:20.5704832Z ###################                                                       26.4%
2019-09-03T21:06:20.5705073Z ######################################################################## 100.0%
2019-09-03T21:06:21.6766893Z extracting /checkout/obj/build/cache/2019-08-13/cargo-beta-x86_64-unknown-linux-gnu.tar.gz
2019-09-03T21:06:21.7348358Z error: failed to resolve patches for `https://github.com/rust-lang/crates.io-index`
2019-09-03T21:06:21.7349344Z Caused by:
2019-09-03T21:06:21.7349522Z   failed to load source for a dependency on `backtrace`
2019-09-03T21:06:21.7349748Z 
2019-09-03T21:06:21.7349924Z Caused by:
2019-09-03T21:06:21.7349924Z Caused by:
2019-09-03T21:06:21.7350349Z   Unable to update /backtrace-rs
2019-09-03T21:06:21.7350798Z Caused by:
2019-09-03T21:06:21.7350798Z Caused by:
2019-09-03T21:06:21.7351168Z   failed to read `/backtrace-rs/Cargo.toml`
2019-09-03T21:06:21.7351604Z Caused by:
2019-09-03T21:06:21.7351776Z   No such file or directory (os error 2)
2019-09-03T21:06:21.7352439Z failed to run: /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path /checkout/src/bootstrap/Cargo.toml
2019-09-03T21:06:21.7353122Z Build completed unsuccessfully in 0:00:27
2019-09-03T21:06:21.7353122Z Build completed unsuccessfully in 0:00:27
2019-09-03T21:06:21.7377629Z == clock drift check ==
2019-09-03T21:06:21.7384617Z   local time: Tue Sep  3 21:06:21 UTC 2019
2019-09-03T21:06:21.8316942Z   network time: Tue, 03 Sep 2019 21:06:21 GMT
2019-09-03T21:06:21.8320322Z == end clock drift check ==
2019-09-03T21:06:42.2675295Z ##[error]Bash exited with code '1'.
2019-09-03T21:06:42.2711173Z ##[section]Starting: Checkout
2019-09-03T21:06:42.2712799Z ==============================================================================
2019-09-03T21:06:42.2712843Z Task         : Get sources
2019-09-03T21:06:42.2712918Z 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)

[alexcrichton]

For some context this is coupled with rust-lang/backtrace-rs#245 being published, and I think the last few commits I've just pushed there may help simplify the integration here (and even delete a bunch of code!)

[alexcrichton]

Ok I've merged that PR and published a new version on crates.io, @cramertj want to update the support here to use it?

[cramertj]

@alexcrichton great, thanks! will do.

[cramertj]

Closing this, as I think a fresh PR would be a better start.