[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>

arch/ppc/boot/lib/Makefile

@@ -4,7 +4,13 @@
 
 CFLAGS_kbd.o	+= -Idrivers/char
 
-lib-y := $(addprefix ../../../../lib/zlib_inflate/, \
+ZLIB_DIR := ../../../../lib/zlib_inflate/
+
+lib-y := $(addprefix $(ZLIB_DIR), \
            infblock.o infcodes.o inffast.o inflate.o inftrees.o infutil.o)
 lib-y += div64.o
 lib-$(CONFIG_VGA_CONSOLE) += vreset.o kbd.o
+
+ifneq ($(KBUILD_SRC),)
+_make_zlib_dir := $(shell [ -d $(obj)/$(ZLIB_DIR) ] || mkdir -p $(obj)/$(ZLIB_DIR) )
+endif