lib: move memcpy()

lib: move memcpy()

By moving the function into an archive, x86 doesn't need to announce
anymore that is has its own implementation - symbol resolution by the
linker will now guarantee that the generic function remains unused, and
the forwarding to the compiler built-in gets done by the common header
anyway.

Allow the function to be individually linkable, discardable, and
overridable.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>