Added more CPUID strings to the ax_gcc_archflag.m4 for skylake i7 chips.

Fixes #473 (closed).

If you have a better way of figuring out all the CPUIDs we are missing than just trial-and-error I'd be interested...

If that was known I doubt this file would be so messy.

I guess the real problem was that the default GCC flags didn't match up to the vectorization flags, which seem to work more reliably.

merged

mentioned in commit bfe5e47c