Initial commit for support of AArch64 in the llvm backend.

[nlewycky]

Description

Enables AArch64 in the llvm backend, and inkwell when the target_arch is aarch64. Adds relevant failing spectests to the excludes.txt.

Review

• Add a short description of the the change to the CHANGELOG.md file

[nlewycky]

bors r+

[bors]

Merge conflict

[nlewycky]

bors r+

[bors]

Build failed

• wasmerio.wasmer

[nlewycky]

bors r+

[bors]

Build failed

• wasmerio.wasmer

[nlewycky]

Given a Cargo.toml with:

[target.'cfg(target_arch = "x86_64")'.dependencies]
git = "https://github.com/TheDan64/inkwell"
rev = "781620e9fa30e51a6e03bd0d49b5f5bb7a782520"
default-features = false
features = ["llvm8-0", "target-x86"]

[target.'cfg(target_arch = "aarch64")'.dependencies]
git = "https://github.com/TheDan64/inkwell"
rev = "781620e9fa30e51a6e03bd0d49b5f5bb7a782520"
default-features = false
features = ["llvm8-0", "target-aarch64"]

when inkwell is built, both target-aarch64 and target-x86 are defined. This is due to rust-lang/cargo#4866. If the underlying LLVM was built without both X86 and AArch64 backends, this will lead to a link error. That's the cause of the windows build failure, that LLVM has the X86 backend but not the AArch64 backend.

[MarkMcCaskey]

@nlewycky I believe we can fix this with the build.rs tricks we did before as long as the target-* inkwell features don't pull in any dependencies in the Cargo.toml, it will work

[nlewycky]

@nlewycky I believe we can fix this with the build.rs tricks we did before as long as the target-* inkwell features don't pull in any dependencies in the Cargo.toml, it will work

I tried implementing this a couple ways, either with build.rs printing cargo:rustc-cfg=feature="target-x86_64" and having target-x86_64 = ["inkwell/target-x86"] in the Cargo.toml, or with build.rs printing cargo:rustc-cfg=feature="inkwell/target-x86" directly. Both times, inkwell is being built without the target being enabled, leading to an attempt to call inkwell::Target::initialize_x86 which isn't declared in inkwell.

[syrusakbary]

bors r+

[bors]

Build failed

• wasmerio.wasmer

[syrusakbary]

bors r+

[syrusakbary]

bors r-

[bors]

Canceled

[syrusakbary]

bors r+

[bors]

Build succeeded

• continuous-integration/travis-ci/push
• wasmerio.wasmer