2026.10.16.3: a configured toolchain for the host's own target is kept; gcc for a glibc target is the glibc payload on aarch64

[Sunrisepeak]

Summary

Inside a Luban system on aarch64, /etc/mcpp/config.toml names gcc@16.1.0 on aarch64-linux-gnu, the system's own gcc. The first mcpp build still downloaded llvm 23.1.3 (266 MB) and did not use the system's gcc (xim-pkgindex#986, editions CI on ubuntu-24.04-arm: target default for aarch64-linux-gnu, replacing your gcc@16.1.0). There were two causes, and both are fixed:

• The row convention replaced a configured pair for the host's own target. [toolchain] default together with a default_target equal to the host triple is now kept (configured_native_pair, in prepare.cppm). A cross target keeps the rule recorded at tc_origin_is_user_explicit (the measured windows-gnu regression), and a capability pin still applies.
• gcc for a glibc target resolved to musl-gcc on aarch64. gcc_native_payload_is_musl now returns the glibc payload for a target that names gnu. xim:gcc has published aarch64 since 16.1.0, and it is the gcc a Luban system has. With no target, aarch64 still uses musl-gcc.

Version 2026.10.16.3, with a CHANGELOG entry. The bundled xlings stays at 2026.10.16.2.

Test

• Unit:
  • new LinuxDefaults.AConfiguredPairForTheHostsOwnTargetKeepsItsToolchain (native pair kept; --target, mcpp's first-run guess and a cross target are not kept);
  • ToolchainRegistry.NativeGccPayloadFollowsWhatTheArchActuallyPublishes updated (an aarch64 gnu target uses glibc gcc, a musl target and no target use musl-gcc).
• After the release, the end-to-end check is xim-pkgindex#986's arm editions job: inside core, mcpp builds with the system's gcc.

Co-authored-by: speak-agent 248744407+speak-agent@users.noreply.github.com