Allow build architecture for x86 other than native

[kreuzerkrieg]

At this moment the -march flag is set in the make file (spdk.common.mk file) as -march=native and there is no way to override it. It may be problematic, since the build machine and staging/production may be of different architecture, though it is still x86. For example, build machine may support AVX512 and will generate the assembly accordingly. It will result in SIGILL on machine that has no support for AVX512.

[darsto]

Bug scrub: We could add a configure option to select the target architecture and pass the same option to underlying libs.

[benlwalker]

Fixed by 7dbdf87. There are more patches in the works to enable full cross compilation to any target, but that is sufficient to target a specific x86 platform instead of native.