Workaround is to not include 64 bit related files, as it is only
building the float/double interfaces, and avoids the build failure:
/usr/include/c++/6.1.1/type_traits: In instantiation of 'struct std::make_unsigned<__int128 unsigned>':
/usr/include/givaro/modular-int64.h:46:60: required from 'class Givaro::Modular<long int, __int128 unsigned>'
/usr/include/givaro/modular-int64.inl:32:46: required from here
/usr/include/c++/6.1.1/type_traits:1820:62: error: invalid use of incomplete type 'class std::__make_unsigned_selector<__int128 unsigned, false, false>'
