repc is not deterministic

Order of qRegisterMetaType changes randomly in generated output. Those types seem to be stored in a QSet which in turn holds them in QHash and the hash is randomly seeded so the order may change between runs.

This means the builds are not reproducible and it also causes unnecessary recompilation for tools like ccache since it sees the file has changed.

Perhaps repc could set QT_HASH_SEED=0 environment variable at startup to avoid this.