[PATCH] ppc: fix build with O=$(output_dir)

[PATCH] ppc: fix build with O=$(output_dir)

Recent changes to arch/ppc/boot/lib/Makefile cause

      CC      arch/ppc/boot/lib/../../../../lib/zlib_inflate/infblock.o
    Assembler messages:
    FATAL: can't create arch/ppc/boot/lib/../../../../lib/zlib_inflate/infblock.o: No such file or directory

when building a ppc kernel using O=$(output_dir) with CONFIG_ZLIB_INFLATE=n,
because the $(output_dir)/lib/zlib_inflate directory doesn't get created.

This patch, which makes arch/ppc/boot/lib/Makefile create the
directory if needed, is one fix for the problem.

Signed-off-by: Roland Dreier <roland@topspin.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>