cpp: Support new archive signing flag
* lang/cpp/src/global.h (enum SignatureMode): Add constant SignArchive. * lang/cpp/src/context.cpp (sigmode2sigmode): Rename to sigflags2sigflags (sigflags2sigflags): ... and rename argument mode to flags and treat it as flags. Adjust the callers. (operator<<): Change local CHECK macro to handle flags. Add new flag to debug stream. * lang/cpp/src/signingresult.cpp (CreatedSignature::mode): Handle new flags (even if it cannot occur currently).
- GnuPG-bug-id: T6342