x86 merge fallout: uml

Don't undef __i386__/__x86_64__ in uml anymore, make sure that (few) places
that required adjusting the ifdefs got those.

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