Fix Zstd x86 kernel build with -march=<specific>
Disable Zstd experimental support for BMI intrinsics, when built with
-march=foo supporting such intrinsics, to avoid attempting to include
immintrin.h. If a later Zstd marks the support non-experimental, we may want
to revisit this approach.
Submitted by: jkim
Reported by: jkim, "Oliver Hartmann" <ohartmann AT walstatt.org>