make O=/dir TAGS

  fails with:

    MAKE   TAGS
  find: security/selinux/include: No such file or directory
  find: include: No such file or directory
  find: include/asm-i386: No such file or directory
  find: include/asm-generic: No such file or directory

  The problem is in this line:
  ifeq ($(KBUILD_OUTPUT),)

KBUILD_OUTPUT is not defined (ever) after make reruns itself.  This line is
used in the TAGS, tags, and cscope makes.

Signed-off-by: George Anzinger <george@mvista.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>