v0.12.0 — i686 and wasm32 legs: gcc.yml arch x86, and emscripten.yml

Two 32-bit targets, for the code that takes size_t to be 64 bits, alignof(std::int64_t) to be 8, or __int128 to exist. Every leg before this one builds for a 64-bit target, where none of that shows. The two targets fail differently, so each catches what the other cannot (#57, #58).

Target	Workflow	size_t	alignof(std::int64_t) in a class	__int128	Tests run under
i686	gcc.yml with arch: x86	unsigned int	4	no	the runner, natively
wasm32	emscripten.yml	unsigned long	8	yes	node

gcc.yml takes arch

arch: x86 does four things:

• adds -m32;
• installs the GCC's multilib through install-gcc's new multilib input;
• builds the dependencies from the new x86-linux-gcc overlay triplet;
• ignores vcpkg_triplet, since the leg has its own triplet.

The trunk snapshot has no 32-bit runtime, so an i686 ladder names released rungs only. The default, x64, builds exactly as before.

emscripten.yml is new

It takes one Emscripten release, emsdk_version (default 6.0.12), rather than a ladder, and builds Debug by default. Its dependencies come from wasm32-emscripten-eh, vcpkg's community triplet with exceptions compiled in, and node from the emsdk runs the tests. It accepts the same vcpkg_features, cxx_flags, scan_for_modules, debug_flags and cmake_args as the other ladders, plus linker_flags, whose default turns on memory growth, an 8 MB stack and EXIT_RUNTIME. Its gate is <job> / all.

To add both legs

  i686:
    uses: rhalbersma/cpp-ci/.github/workflows/gcc.yml@<sha> # v0.12.0
    with:
      arch: x86
      tiers: stable
      build_types: Debug

  wasm32:
    uses: rhalbersma/cpp-ci/.github/workflows/emscripten.yml@<sha> # v0.12.0

No existing check names change

The ladders resolve as in v0.11.1. gcc.yml's vcpkg cache key now carries the arch, so the first run after the bump rebuilds the dependencies once. The internal actions are repinned to #57's commit. Both legs ran green on xstd-ints (rhalbersma/xstd-ints#284) and xstd-misc (rhalbersma/xstd-misc#39) before this tag.