sandybridge: Does not compile with -dnoopt

[bluss]

The sandybridge configuration does not compile with -dnoopt, it requires avx.

The following would fix it:

COPTFLAGS      := -O0 -march=native

Sample error, using gcc (gcc version 5.3.1 20160316 (Debian 5.3.1-12))

config/sandybridge/kernels/3/bli_gemm_int_d8x4.c: In function ‘bli_dgemm_int_8x4’:
config/sandybridge/kernels/3/bli_gemm_int_d8x4.c:111:10: warning: AVX vector return without AVX enabled changes the ABI [-Wpsabi]
  va0_3b0 = _mm256_setzero_pd();
          ^
In file included from /usr/lib/gcc/x86_64-linux-gnu/5/include/immintrin.h:41:0,
                 from config/sandybridge/kernels/3/bli_gemm_int_d8x4.c:36:
/usr/lib/gcc/x86_64-linux-gnu/5/include/avxintrin.h:834:1: error: inlining failed in call to always_inline ‘_mm256_load_pd’: target specific option mismatch
 _mm256_load_pd (double const *__P)
 ^

[bluss]

This was fixed. Thanks a lot!