[vcpkg] Support cross compile arm64-linux, arm-linux triplets on a linux x86_64 host.

[x-projs]

Describe the pull request

• What does your PR fix?
  Support cross compile arm64-linux, arm-linux triplets on a linux x86_64 host.

• Which triplets are supported/not supported? Have you updated the CI baseline?
  Support arm64-linux and arm-linux triplets.

• Does your PR follow the maintainer guide?
  Yes

[Neumann-A]

Personal opinion: All those crosscompiling toolchains should have seperate toolchains and not be cramped into a single universal linux one.

[kevinlul]

I did something related to this in #11535 but only for an autoconf system for that specific port. Not sure if that would be related though. In that case I depend on the cross-compiler toolchain file.

[x-projs]

Where should we put the cross-compiler toolchain file? If we ask user to supply it, user might not know how to generate it. Ideally, in most of cases, user only need few additional efforts to make cross compiling work.

[kevinlul]

I'm referring to cmake .. -DCMAKE_TOOLCHAIN_FILE=path/to/vcpkg/scripts/buildsystems/vcpkg.cmake -DVCPKG_CHAINLOAD_TOOLCHAIN_FILE=some/cmake/toolchain/for/crosscompiler

[x-projs]

But how does it work with ./vcpkg install ...? Seems we can't pass -DVCPKG_CHAINLOAD_TOOLCHAIN_FILE=some/cmake/toolchain/for/crosscompiler to vcpkg install.

[Neumann-A]

But how does it work with ./vcpkg install ...? Seems we can't pass -DVCPKG_CHAINLOAD_TOOLCHAIN_FILE=some/cmake/toolchain/for/crosscompiler to vcpkg install.

You add it into the triplet.
Simply use set(VCPKG_CHAINLOAD_TOOLCHAIN_FILE <sometoolchainpath>) in the triplet

[ras0219-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ras0219-msft]

I think this is the right incremental improvement.

Once complexity increases enough, it may make sense to have separate files for each of the different X-to-Y cross targets; however right now we support all Linux targets out of a single file (linux.cmake). Furthermore, the detection of which X-to-Y file to select still would need to exist somewhere. Finally, our toolchain hashing system currently supports only hashing one file for the toolchain and doesn't have a mechanism to determine which specific combo was loaded.

For all these reasons, this looks like a good improvement for our current state and will help inform more improvements into the future.

[JackBoosY]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BillyONeal]

Thanks for your contribution!