x32: make X32, !IA32_EMULATION setups able to execute x32 binaries

It's really trivial - the only wrinkle is making sure that
compiler knows that ia32-related side of COMPAT_ARCH_DLINFO
is dead code on such configs (we don't get there without
having passed compat_elf_check_arch(), and on such configs
that'll fail for ia32 binary).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>