Conservatively disable instruction higher instruction sets

[ClementPernet]

#284 points to a problem arising when an instruction set is disabled (AVX) but not some above it (AVX512F).
This causes fflas-ffpack to incorrectly assume that AVX is available, although the compiler is not being passed the -mavx flag.
2 options:

1. change the macros defining which instruction set is available
2. force disable all instruction sets above the one that is explicitely disabled in the M4 script.
   I vote for 2.

[ClementPernet]

Closing as it is no longer relevant since we removed the fine grain selection of intruction sets, and use -march=native instead.