workaround needed for gcc bug (old gcc), defaulted noexcept constructors

[danmar]

GCC fails to compile simplecpp:

externals/simplecpp/simplecpp.cpp:3129:1: error: function 'simplecpp::FileDataCache::FileDataCache(simplecpp::FileDataCache&&)' defaulted on its redeclaration with an exception-specification that differs from the implicit exception-specification ''
 simplecpp::FileDataCache::FileDataCache(FileDataCache &&) noexcept = default;
 ^
externals/simplecpp/simplecpp.cpp:3130:27: error: function 'simplecpp::FileDataCache& simplecpp::FileDataCache::operator=(simplecpp::FileDataCache&&)' defaulted on its redeclaration with an exception-specification that differs from the implicit exception-specification ''
 simplecpp::FileDataCache &simplecpp::FileDataCache::operator=(simplecpp::FileDataCache &&) noexcept = default;
                           ^