Add tracking issue for the unwind attribute

[Mark-Simulacrum]

cc #58760

[rust-highfive]

r? @michaelwoerister

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[rust-highfive]

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

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travis_time:end:14884658:start=1551209049594140408,finish=1551209121431415854,duration=71837275446
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
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---
[01:04:32] 
[01:04:32] ---- [ui] ui/feature-gates/feature-gate-unwind-attributes.rs stdout ----
[01:04:32] diff of stderr:
[01:04:32] 
[01:04:32] - error[E0658]: #[unwind] is experimental
[01:04:32] + error[E0658]: #[unwind] is experimental (see issue #58760)
[01:04:32] 2   --> $DIR/feature-gate-unwind-attributes.rs:11:5
[01:04:32] 3    |
[01:04:32] 4 LL |     #[unwind(allowed)] //~ ERROR #[unwind] is experimental
[01:04:32] 
[01:04:32] The actual stderr differed from the expected stderr.
[01:04:32] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-unwind-attributes/feature-gate-unwind-attributes.stderr
[01:04:32] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-unwind-attributes/feature-gate-unwind-attributes.stderr
[01:04:32] To update references, rerun the tests and pass the `--bless` flag
[01:04:32] To only update this specific test, also pass `--test-args feature-gates/feature-gate-unwind-attributes.rs`
[01:04:32] error: 1 errors occurred comparing output.
[01:04:32] status: exit code: 1
[01:04:32] status: exit code: 1
[01:04:32] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/feature-gates/feature-gate-unwind-attributes.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-unwind-attributes/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-C" "no-prepopulate-passes" "-Cpasses=name-anon-globals" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/feature-gates/feature-gate-unwind-attributes/auxiliary" "-A" "unused"
[01:04:32] ------------------------------------------
[01:04:32] 
[01:04:32] ------------------------------------------
[01:04:32] stderr:
[01:04:32] stderr:
[01:04:32] ------------------------------------------
[01:04:32] {"message":"#[unwind] is experimental (see issue #58760)","code":{"code":"E0658","explanation":"\nAn unstable feature was used.\n\nErroneous code example:\n\n```compile_fail,E658\n#[repr(u128)] // error: use of unstable library feature 'repr128'\nenum Foo {\n    Bar(u64),\n}\n```\n\nIf you're using a stable or a beta version of rustc, you won't be able to use\nany unstable features. In order to do so, please switch to a nightly version of\nrustc (by using rustup).\n\nIf you're using a nightly version of rustc, just add the corresponding feature\nto be able to use it:\n\n```\n#![feature(repr128)]\n\n#[repr(u128)] // ok!\nenum Foo {\n    Bar(u64),\n}\n```\n"},"level":"error","spans":[{"file_name":"/checkout/src/test/ui/feature-gates/feature-gate-unwind-attributes.rs","byte_start":285,"byte_end":303,"line_start":11,"line_end":11,"column_start":5,"column_end":23,"is_primary":true,"text":[{"text":"    #[unwind(allowed)] //~ ERROR #[unwind] is experimental","highlight_start":5,"highlight_end":23}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"add #![feature(unwind_attributes)] to the crate attributes to enable","code":null,"level":"help","spans":[],"children":[],"rendered":null}],"rendered":"error[E0658]: #[unwind] is experimental (see issue #58760)\n  --> /checkout/src/test/ui/feature-gates/feature-gate-unwind-attributes.rs:11:5\n   |\nLL |     #[unwind(allowed)] //~ ERROR #[unwind] is experimental\n   |     ^^^^^^^^^^^^^^^^^^\n   |\n   = help: add #![feature(unwind_attributes)] to the crate attributes to enable\n\n"}
[01:04:32] {"message":"For more information about this error, try `rustc --explain E0658`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0658`.\n"}
[01:04:32] 
[01:04:32] ------------------------------------------
[01:04:32] 
---
[01:04:32] 
[01:04:32] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:496:22
[01:04:32] 
[01:04:32] 
[01:04:32] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--target-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:04:32] 
[01:04:32] 
[01:04:32] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:04:32] Build completed unsuccessfully in 0:04:04
[01:04:32] Build completed unsuccessfully in 0:04:04
[01:04:32] make: *** [check] Error 1
[01:04:32] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:154caac3
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Feb 26 20:30:03 UTC 2019
---
travis_time:end:06f46647:start=1551213004902166235,finish=1551213004906540838,duration=4374603
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:1d2f17d0
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0bdb6298
travis_time:start:0bdb6298
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:10529a9c
$ dmesg | grep -i kill

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[Centril]

r? @Centril
@bors r+ rollup

[bors]

📌 Commit f313bae has been approved by Centril