Add targets for HermitCore (https://hermitcore.org) to the Rust compiler and port libstd to it.

[ColinFinck]

As a start, the port uses the simplest possible configuration (no jemalloc, abort on panic) and makes use of existing Unix-specific code wherever possible.
It adds targets for x86_64 (current main HermitCore platform) and aarch64 (HermitCore platform under development).

Together with the patches to "liblibc" (rust-lang/libc#1048) and llvm (rust-lang/llvm#122), this enables HermitCore applications to be written in Rust.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @bluss (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[ColinFinck]

This patch is part of a patch series to add HermitCore support to Rust:

1. Add support for writing HermitCore (https://hermitcore.org) ELF binaries llvm#122 / https://reviews.llvm.org/D48964
2. Add libc definitions for HermitCore (https://hermitcore.org) libc#1048
3. Add targets for HermitCore (https://hermitcore.org) to the Rust compiler and port libstd to it. #52861

CC @stlankes

[rust-highfive]

The job x86_64-gnu-llvm-5.0 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.

Click to expand the log.

[00:03:48] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:49] tidy error: /checkout/src/libstd/sys/unix/condvar.rs:88: line longer than 100 chars
[00:03:49] tidy error: /checkout/src/liballoc_system/lib.rs:177: line longer than 100 chars
[00:03:49] tidy error: /checkout/src/liballoc_system/lib.rs:200: line longer than 100 chars
[00:03:50] some tidy checks failed
[00:03:50] 
[00:03:50] 
[00:03:50] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:50] 
[00:03:50] 
[00:03:50] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:50] Build completed unsuccessfully in 0:00:49
[00:03:50] Build completed unsuccessfully in 0:00:49
[00:03:50] Makefile:79: recipe for target 'tidy' failed
[00:03:50] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0c18872c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:18330cb7:start=1532959497117513239,finish=1532959497127160315,duration=9647076
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:06fe3f20
$ 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 -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:0c719900
travis_time:start:0c719900
$ 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:05fecfec
$ dmesg | grep -i kill

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]

Thanks! Looks like there's a tidy error on CI but otherwise this looks good to merge!

[ColinFinck]

@alexcrichton Thanks for the prompt reply! I've fixed the coding style.

[alexcrichton]

@bors: r+ rollup

[bors]

📌 Commit 4ad4ad0 has been approved by alexcrichton