GCC 11 will support x86_64 micro-architecture feature levels.
What we really want to support is nehalem or newer, which is x86-64-v2,
and specifying this instead of nehalem means that we are not tuning for
nehalem specifically.
Nehalem is the minimum requirement for the host application as it makes
use of SSE4.1 instructions, as such we should default to compling with
it instead of `-march=native` so that when the binary is distributed it
will operate on foreign systems.
Fixed#416
