_addcarry_u64 and _addcarryx_u64 with MSVC and ICC

Related, GCC does not support ADOX and ADCX at the moment. “At the moment” includes GCC 6.4 (Fedora 25) and GCC 7.1 (Fedora 26). GCC effectively disabled the intrinsics, but it still advertises support by defining __ADX__ in the preprocessor. Also see Issue 67317, Silly code generation for _addcarry_u32/_addcarry_u64. Many thanks to Xi Ruoyao for … Read more