toolchain::SysrootHandle

Consumer-facing aggregate of every component a Toolchain depends on.

Detailed description

The service returns one from `waitFor()` after all components are ready. Consumers read the include / library paths + archive list + flag bundles and feed them straight into their compiler/linker invocations. Identity comes from the toolchain it was built for; two handles for the same `toolchainId` + `revisionToken` are equivalent.