Add HarmonyOS (OHOS) community triplets

[jobor]

Summary

Add HarmonyOS / OpenHarmony (OHOS) as a cross-compilation target in vcpkg with community triplets, a toolchain file, and platform detection — similar to existing Android and iOS support.

Motivation

HarmonyOS uses a Clang/LLVM-based NDK-style toolchain for native C/C++ development and is seeing significant adoption. We (The Qt Company) are porting Qt to HarmonyOS and need to cross-compile third-party dependencies for this target. We have a working implementation that we've been using in production:

• Blog post: https://www.qt.io/blog/building-libraries-for-harmonyos-with-vcpkg
• vcpkg registry fork: https://git.qt.io/qtbuildsystem/vcpkg/-/tree/ohos
• vcpkg-tool fork: https://git.qt.io/qtbuildsystem/vcpkg-tool/-/tree/ohos

Proposed changes

vcpkg-tool: Add ohos as a recognized platform identifier for supports expressions (one commit).

vcpkg registry:

• Toolchain file (scripts/toolchains/ohos.cmake) that delegates to the SDK's native toolchain. Requires setting an environment variable OHOS_SDK_ROOT (SDK with API 12+).
• Three community triplets: arm64-ohos, arm-ohos, x64-ohos — all producing dynamically linked libraries.
• Port patches for libraries needing OHOS-specific adjustments (currently: libpng, fontconfig, ICU). This could be contributed separately as well.

Note that we use ohos (not harmonyos) in all identifiers, consistent with the SDK's own naming and keeping triplet names short.

Structurally similar to the Xbox community triplet addition in #29210.

Questions before we submit PRs

1. Is ohos acceptable as the VCPKG_CMAKE_SYSTEM_NAME / supports term?
2. Should the vcpkg-tool change be merged first, or can it be coordinated with the registry PR?
3. Single PR (triplets + toolchain + port patches) or separate PRs?

Ready to submit once we have feedback on the approach.

[2088782983]

+1

[MouriNaruto]

I have read the implementations by you, in general, looks good. Hope that can be merged finally. But I also need to show my opinions.

• I hope we can have the new VCPKG_CMAKE_SYSTEM_NAME, but I don't know what's the opinions from vcpkg guys, but I know if they don't accept adding new VCPKG_CMAKE_SYSTEM_NAME, we can use Linux instead, maybe it's the way to reduce frictions. (I can prove that because I had made overlay triplets for OHOS targets at https://github.com/qietv/vcpkg-ohos-overlay/tree/main/triplets)
• I think the OHOS community triplets should have the static variants for compiling static libraries, which is really useful.

Kenji Mouri

[yangyongzhen]

+1,good news ,Hope that can be merged finally!

[liangqi]

@BillyONeal would you like to review this request and give some feedback? Thanks in advance.

[jobor]

I've created a pull request for the platform support / community triplets now: #51470

[jobor]

Pull request for vcpkg-tool is here: microsoft/vcpkg-tool#2004