Remove configure checks for supported instruction sets

Remove configure checks for supported instruction sets

These were checking whether the instruction set is supported by
the host CPU, however they were only used to condition on whether
this instruction set is targeted at all. It would still use dynamic
dispatch (e.g. based on ifunc resolvers) to select the actual
implementation. Whether the target is guaranteed to support the
instruction set without dispatch is determined based on pre-defined
macros like __SSE2__.

This removes the configure-time builtin cpu checks to remove
confusion. Additionally this allows targeting an architecture that
is newer than the host architecture.