[arch][x86] drop march to x86-64
[arch][x86] drop march to x86-64

-march=x86-64-v2 is not supported on old compilers.

Can fix in the future, but for the moment may as well just drop -v2
since it's not really being used.

hollanderic/lkstuff,littlekernel/lk,hollanderic/lkstuff,littlekernel/lk,littlekernel/lk,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff