Enable "full tools" option on ARM dist builders

[alexcrichton]

This commit switches the --enable-extended option on the arm-related
dist builders to --enable-full-tools. This alias in config.py
corresponds to enabling a few more options:

• rust.lld = true - this is the main purpose of this PR, to enable LLD
  on ARM-related platforms. This means it will effectively unlock
  compilation of wasm programs from an arm host.

• rust.llvm-tools = true - it turns out that this option is largely
  ignored in rustbuild today. This is only read in one location to set
  some flags for the llvm-tools package, but the llvm-tools package
  is already produced on all of these builders. It's predicted that this
  will have no effect on build times.

• rust.codegen-backends = ['llvm'] - historically this also enabled
  the emscripten backend, but that has long since been removed.

This brings the ARM dist builders in line with the x86_64 dist builders
using this flag. The hope is that the extra time spent on CI building
LLD will acceptable because it's cached by sccache, LLD is a
relatively small C++ project, and the dist builders are all clocking
well under 3 hours (the slowest of all builders) around 2 hours.

There's likely some possible cleanup that can happen with these
configure options since it doesn't look like they've aged too too well,
but I'm hopeful that possible refactorings, if necessary, could be
deferred to future PRs.

[rust-highfive]

r? @kennytm

(rust_highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

These changes look reasonable to me. I'm unsure if we want some form of approval (e.g. FCP) though -- seems like given this amounts to adding lld I don't think it's necessary.

r=me if you feel the same way.

r? @Mark-Simulacrum

[alexcrichton]

I would agree yeah that this probably doesn't need a full sign-off. How about the following though to account for that:

• Merge now w/o FCP
• I'll watch the builds after this lands
• If the build time increase is >10m, I'll revert and we can figure out something else, otherwise this'll slide in.

[Mark-Simulacrum]

Seems reasonable to me. We're also migrating to GHA over the next month or so so slight losses are likely to be patched over by the 2 (or more) times faster builds there so I'm not too worried.

@bors r+

[bors]

📌 Commit c7a7658 has been approved by Mark-Simulacrum

[alexcrichton]

@bors: r-

I've got some build logic to work through, this won't work as-is.

[alexcrichton]

Ok I pushed up another commit after getting a successful build of LLD for aarch64. @Mark-Simulacrum wanna take a look at this again?

[Mark-Simulacrum]

That indeed looks like a pretty horrible hack, but if it works seems fine. If an LLVM upgrade breaks this we may need to drop it temporarily, but given how long those usually take, it's probably not too likely.

@bors r+

[bors]

📌 Commit 0546d11 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 0546d11 with merge 4307e4ad6681e80e1fd0b447c62fed384cf7a57f...

[bors]

💔 Test failed - checks-azure

[kennytm]

@bors retry

https://dev.azure.com/rust-lang/rust/_build/results?buildId=27670&view=logs&j=aac1e68a-9baa-54d2-b80b-75ce793a8506&t=bd3d1d78-06ce-563d-23c4-bd941b41a778

Chocolatey timed out waiting for the command to finish. The timeout 
 specified (or the default value) was '2700' seconds. Perhaps try a 
 higher `--execution-timeout`? See `choco -h` for details.
The install of msys2 was NOT successful.

[bors]

⌛ Testing commit 0546d11 with merge 851098390128b82e3519fe93b8c88be2115a9359...

[Dylan-DPC-zz]

@bors retry yield

[bors]

⌛ Testing commit 0546d11 with merge 825cf51...

[bors]

☀️ Test successful - checks-azure
Approved by: Mark-Simulacrum
Pushing 825cf51 to master...

[alexcrichton]

Ok so looking at the build just before this and just after this the numbers sort of go both ways (some arm builders got faster, some slower). I think it's all largely within variance though.

Looking at the timing specifically of building LLD, it looks like we do indeed have a wasteful build of LLD for the host platform, but otherwise it only takes 20s (cached) to build LLD, so that's not so bad in a 3h build.