build: configure seastar compiler with right -march flag
build: configure seastar compiler with right -march flag

We set -march=nehalem to get a cross-microarch binary that supports the
crc32 instruction, but we don't configure seastar with that flag; so seastar
instead inherits dpdk's default, which is -march=native.  The resulting
binary may not run on hosts other than the one it was compiled on.

Fix by passing the flag to seastar and inheriting it from there.

Fixes #338.

senseb/scylla,capturePointer/scylla,avikivity/scylla,kjniemi/scylla,scylladb/scylla,scylladb/scylla,eklitzke/scylla,wildinto/scylla,avikivity/scylla,dwdm/scylla,tempbottle/scylla,bowlofstew/scylla,duarten/scylla,rluta/scylla,acbellini/scylla,duarten/scylla,gwicke/scylla,glommer/scylla,capturePointer/scylla,rluta/scylla,senseb/scylla,guiquanz/scylla,avikivity/scylla,stamhe/scylla,raphaelsc/scylla,respu/scylla,kjniemi/scylla,asias/scylla,duarten/scylla,eklitzke/scylla,aruanruan/scylla,phonkee/scylla,rentongzhang/scylla,justintung/scylla,gwicke/scylla,wildinto/scylla,respu/scylla,scylladb/scylla,kangkot/scylla,raphaelsc/scylla,victorbriz/scylla,shaunstanislaus/scylla,gwicke/scylla,linearregression/scylla,glommer/scylla,justintung/scylla,asias/scylla,phonkee/scylla,dwdm/scylla,kjniemi/scylla,acbellini/scylla,guiquanz/scylla,rentongzhang/scylla,respu/scylla,acbellini/scylla,phonkee/scylla,kangkot/scylla,guiquanz/scylla,wildinto/scylla,raphaelsc/scylla,aruanruan/scylla,victorbriz/scylla,eklitzke/scylla,capturePointer/scylla,senseb/scylla,kangkot/scylla,tempbottle/scylla,asias/scylla,linearregression/scylla,linearregression/scylla,bowlofstew/scylla,stamhe/scylla,stamhe/scylla,glommer/scylla,dwdm/scylla,victorbriz/scylla,tempbottle/scylla,rluta/scylla,scylladb/scylla,shaunstanislaus/scylla,rentongzhang/scylla,justintung/scylla,shaunstanislaus/scylla,bowlofstew/scylla,aruanruan/scylla