[PATCH] uml: readd missing define to arch/um/Makefile-i386

scripts/Makefile.build:13: /Makefile: No such file or directory
scripts/Makefile.build:64: kbuild: Makefile.build is included improperly

the define was removed, but its still required to build some targets.

Signed-off-by: Olaf Hering <olh@suse.de>
Cc: Paolo Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>