int128 on OSX and fedora

[ClementPernet]

The config detect scripts not only look for existence of __int128_t but also verifies whether std::make_unsigned<__int128_t>::type is defined.
This fails on OSX and fedora although both types __int128_t and __uint128_t are defined.
FFLAS-FFPACK decides whether it supports int128 based on Givaro's detection. As a consequence simd256<int64_t>::mulhi can not be defined although it does not use the std::make_unsigned machinery.

[ClementPernet]

Suggestion:

• decouple detection of int128_t from the capacity to do std::make_unsigned<int128_t>
• when std::make_unsigned<int128_t> is not defined, couldn't we force define it in Givaro?

[ClementPernet]

For the record, I have already decoupled FFLAS-FFPACK detection of int128 from that of Givaro, since fflas-ffpack does not require the ability to do std:make_unsigned<__int128_t>

[shobhittya]

fatal error: givaro/givzpz.h: No such file or directory
#include <givaro/givzpz.h>
how to remove this error?