Fix build of security/gpgme-qt5 with gcc49

In file included from qgpgmebackend.cpp:42:0:
../../../lang/cpp/src/engineinfo.h: In constructor

'GpgME::EngineInfo::Version::Version(const string&)':

../../../lang/cpp/src/engineinfo.h:47:17: error: 'sscanf' is not a

member of 'std'
    std::sscanf(version.c_str(), "%d.%d.%d", &major, &minor, &patch) != 3) {

PR: 214687
Submitted by: tcberner