llvm.libcxx 22.1.8.1, and llvm.compiler-rt-builtins 22.1.8.3 with the Apple rows (mcpp#630)

[Sunrisepeak]

Two source packages for the iOS rows (mcpp-community/mcpp#630, item 4), each mirrored on GitCode and verified byte for byte against the GitHub tag archive:

• llvm.libcxx 22.1.8.1 (new): libc++ and libc++abi as a source package with a std module, for a hosted target whose toolchain payload cannot supply a static libc++ built for it. On the iOS rows the payload's archives are macOS objects and the engine linked the SDK's libc++ under the payload's newer headers; a program using std::unordered_map<std::string, int> failed at link on __hash_memory. Repository: https://github.com/mcpplibs/libcxx
• llvm.compiler-rt-builtins 22.1.8.3: the Apple rows. The payload carries libclang_rt.osx.a and no ios/iossim archive, so __isPlatformVersionAtLeast was undefined at link; the package now carries upstream's Darwin selection under cfg(os = "ios"). Pull request: 22.1.8.3: the Apple rows, whose payload carries no compiler runtime for the platform compiler-rt-builtins#1.

An iOS application declares both:

[target.'cfg(os = "ios")'.dependencies]
llvm.libcxx               = "22.1.8.1"
llvm.compiler-rt-builtins = "22.1.8.3"

The engine side (the C++ layer answering for its own headers, the graph runtime on a prebuilt C library) is in the mcpp batch for #630; the packages build and report correctly on the released engine as well (the builtins package's macOS CI ran on 2026.9.13.1).

Design record: mcpp-community/mcpp .agents/docs/2026-09-13-630-what-a-framework-still-hits-in-the-engine.md, §5.