x86-64: fix overlap of modules and fixmap areas

commit 66d4bdf2 upstream

Plus add a build time check so this doesn't go unnoticed again.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>