x86, 32-bit: add some compile time checks to mem_init()

Some of the inconsistencies checked for at run time can be detected at
build time already, so duplicate the checks done at run time to also be
done at build time.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>