fossilize: codeCacheBlobPath is shared across concurrent platform builds — race condition if host is one of many platforms

Trap: createBinaryForPlatform runs concurrently for all platforms. The code-cache blob path (codeCacheBlobPath) is a fixed path derived from the config, not per-platform. If the host platform is included in a multi-platform build, concurrent runs could race on reading/writing the blob file. Looks safe because only the host branch writes it, but concurrent reads from other platforms during the write window are possible. Fix: generate the host blob sequentially before spawning concurrent platform builds, or use a per-run temp path.