Add builtin targets for mips64(el)-unknown-linux-muslabi64

[xen0n]

This is prerequisite for rust-lang/libc#1449.

Tested locally to produce working static and dynamic binaries, but CI config is untested for now CI is to be added in a follow-up PR.

edit: dynamic binaries also confirmed working!

edit 2: changed triples to include ABI, and removed stray crt_static_default = false declarations to be consistent with other musl targets

[rust-highfive]

r? @eddyb

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[xen0n]

This is ready for review, for unblocking the libc changes.

[xen0n]

r? @alexcrichton

[alexcrichton]

@bors: r+

[bors]

📌 Commit e1bd8cb has been approved by alexcrichton

[bors]

⌛ Testing commit e1bd8cb with merge 0329c99a420dfdb7914c64875fbdc4c1b892e301...

[bors]

💔 Test failed - checks-azure

[rust-highfive]

The job dist-x86_64-musl 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.

2019-08-09T18:58:18.5153259Z do so (now or later) by using -b with the checkout command again. Example:
2019-08-09T18:58:18.5153308Z 
2019-08-09T18:58:18.5153547Z   git checkout -b <new-branch-name>
2019-08-09T18:58:18.5153603Z 
2019-08-09T18:58:18.5153892Z HEAD is now at 0329c99a4 Auto merge of #63165 - xen0n:mips64-musl-targets, r=alexcrichton
2019-08-09T18:58:18.5313819Z ##[section]Starting: Collect CPU-usage statistics in the background
2019-08-09T18:58:18.5316707Z ==============================================================================
2019-08-09T18:58:18.5316810Z Task         : Bash
2019-08-09T18:58:18.5316876Z Description  : Run a Bash script on macOS, Linux, or Windows
---
2019-08-09T21:07:40.0677910Z     Finished release [optimized] target(s) in 5m 20s
2019-08-09T21:07:40.0840987Z [TIMING] ToolBuild { compiler: Compiler { stage: 1, host: "x86_64-unknown-linux-musl" }, target: "x86_64-unknown-linux-musl", tool: "rls", path: "src/tools/rls", mode: ToolRustc, is_optional_tool: true, source_type: Submodule, extra_features: ["clippy"] } -- 320.848
2019-08-09T21:07:59.0686344Z 
2019-08-09T21:07:59.0688007Z 
2019-08-09T21:07:59.0689732Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-musl/stage0-tools-bin/fabricate" "generate" "--product-name=Rust" "--rel-manifest-dir=rustlib" "--success-message=RLS-ready-to-serve." "--image-dir" "/checkout/obj/build/tmp/dist/rls-image" "--work-dir" "/checkout/obj/build/tmp/dist" "--output-dir" "/checkout/obj/build/dist" "--non-installed-overlay" "/checkout/obj/build/tmp/dist/rls-overlay" "--package-name=rls-nightly-x86_64-unknown-linux-musl" "--legacy-manifest-dirs=rustlib,cargo" "--component-name=rls-preview"
2019-08-09T21:07:59.0690489Z expected success, got: signal: 11
2019-08-09T21:07:59.0690903Z 
2019-08-09T21:07:59.0693928Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap dist --build x86_64-unknown-linux-musl
2019-08-09T21:07:59.0694383Z Build completed unsuccessfully in 2:01:25
2019-08-09T21:07:59.0694383Z Build completed unsuccessfully in 2:01:25
2019-08-09T21:08:02.7663572Z ##[error]Bash exited with code '1'.
2019-08-09T21:08:02.7699022Z ##[section]Starting: Upload CPU usage statistics
2019-08-09T21:08:02.7710334Z ==============================================================================
2019-08-09T21:08:02.7710447Z Task         : Bash
2019-08-09T21:08:02.7710518Z Description  : Run a Bash script on macOS, Linux, or Windows

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]

@bors: retry

[bors]

⌛ Testing commit 30fcd50 with merge f7af19c...

[bors]

☔ The latest upstream changes (presumably #63592) made this pull request unmergeable. Please resolve the merge conflicts.

[pietroalbini]

@bors retry r-

[smaeul]

---

EDIT: Ignore me (see the next comment).

---

@xen0n The default ABI for an architecture shouldn't have a suffix, and the names for alternative ABIs are generally standardized by the architecture vendor.

32-bit ARM targets have an eabi suffix to their environment only for unfortunate historical reasons: because the ARM EABI, or "embedded" ABI was so much better than the original ARM ABI, everyone stopped using the old ARM ABI. The EABI became the only/default ABI several years later.

For MIPS64 targets, the 64-bit ABI with hard float is the default. So these two targets should have been named

mips64-unknown-linux-musl
mips64el-unknown-linux-musl

like they were originally. @alexcrichton, I'm guessing this is impossible to fix now? Or could this still be fixed since rust-lang/libc#1449 was merged after the latest release?

For completeness, the other possibilities would be:

mips64-unknown-linux-musln32
mips64-unknown-linux-musln32sf
mips64el-unknown-linux-musln32
mips64el-unknown-linux-musln32sf

[smaeul]

Sorry, MIPS ABI selection is more of a mess than I realized. The gnuabi64 and gnuabin32 environments appear to be Debianisms. In clang/LLVM, mips64-unknown-linux-gnu and mips64-unknown-linux-gnuabi64 are exact aliases of each other. The only reference to abi64 in gcc is in the context of Debian-style multiarch.

In vanilla gcc, the triple is not parsed to determine the ABI. It simply defaults to n32. However, in musl-cross-make, the "blessed" tool for making musl-targeting toolchains, mips64-unknown-linux-musl means --with-abi=64.

Presumably this sort of confusion is what led Debian to start adding the abi64 suffix. So while I don't think the abi64 suffix is strictly necessary, since it's the default in LLVM and any musl-targeting gcc, it's not wrong, and the rust triple is fine as-is.

[alexcrichton]

Targets aren't really set in stone and have been renamed from time to time. It basically just involves asking the community of those using the targets if they agree with the rename.