Add Linux LoongArch 64-bit support

[cheungxi]

Summary

Add prebuilt libvips support for Linux LoongArch 64-bit (linux-loong64).

Changes

• Add an Ubuntu 24.04-based LoongArch cross-compilation environment.
• Use the Ubuntu GCC 14 LoongArch cross-toolchain.
• Add CMake and Meson cross-compilation configuration.
• Configure the Rust loongarch64-unknown-linux-gnu target.
• Add the @img/sharp-libvips-linux-loong64 npm package.
• Add linux-loong64 to the build script, CI matrix, npm workspaces and documentation.
• Enable Highway SIMD support using the LSX baseline with optional LASX runtime dispatch.
• Declare a minimum glibc version of 2.39, matching the Ubuntu 24.04 build sysroot.

Validation

• Completed a full linux-loong64 cross-build on an x86_64 Ubuntu host.
• Successfully built libvips 8.18.5 and all enabled dependencies, including:
  • zlib-ng LoongArch optimisations
  • libffi LoongArch assembly
  • librsvg using the Rust LoongArch target
  • libheif and UltraHDR
• Verified the resulting library is a LoongArch 64-bit ELF shared object.
• Verified that only the expected system libraries remain dynamically linked:
  • libstdc++.so.6
  • libm.so.6
  • libgcc_s.so.1
  • libc.so.6
  • ld-linux-loongarch-lp64d.so.1
• Tested the generated library on a native LoongArch system:
  • vips_init() returned 0
  • vips_version() returned 8.18.5
• The build-linux-loong64 GitHub Actions job completed successfully and uploaded its
  artifact.

CI validation run:

https://github.com/cheungxi/sharp-libvips/actions/runs/32037607798

[lovell]

Hello, thank you for the PR.

As you've seen, this repo cross-compiles libvips binaries for various platforms and architectures. However the sharp repo uses QEMU-based emulation via uraimo/run-on-arch-action where native builds are unavailable. This does not currently support LoongArch CPUs so I am unable to merge and support this change at present.

[cheungxi]

Hello, thank you for the PR.

As you've seen, this repo cross-compiles libvips binaries for various platforms and architectures. However the sharp repo uses QEMU-based emulation via uraimo/run-on-arch-action where native builds are unavailable. This does not currently support LoongArch CPUs so I am unable to merge and support this change at present.

Thank you. LoongArch64 support has now been merged and released in
run-on-arch-action v3.2.0:

https://github.com/uraimo/run-on-arch-action/releases/tag/v3.2.0

The action's LoongArch64 CI is passing:

https://github.com/uraimo/run-on-arch-action/actions/runs/32153980328

I will also prepare an end-to-end sharp QEMU build using a glibc
linux/loong64 image. Could you please confirm whether the action release
removes the platform-support blocker for this PR?