Should not default to -march=native

[jschueller]

By default METIS (& GKlib) are compiled with march=native which can cause errors like:
Program terminated with signal SIGILL, Illegal instruction.
https://github.com/KarypisLab/METIS/blob/master/conf/gkbuild.cmake#L39
this should be an opt-in option

[wshtx]

@jschueller thanks, I just encounter the same problem after I tranfer a execute program compiled in a server to another server.