[patch] Makefile: can't build modules outside the kernel tree if it was built using O=

[Caveh Jalali <ecaveh@gmail.com>]

in 2.6.31, it is no longer possible to build kernel modules for some platforms
(the ones that need include2) outside the kernel src tree if the
src tree was built using O= to specify an alternate directory for the
build output.

i think this broke with the following commit:

commit b8b572e1015f81b4e748417be2629dfe51ab99f9
Author: Stephen Rothwell <sfr@canb.auug.org.au>
Date:   Fri Aug 1 15:20:30 2008 +1000

   powerpc: Move include files to arch/powerpc/include/asm


when the platform specific include directories were shuffled around
without updating the
top level Makefile.  however, i think this FAIL is generic, and not
limited to powerpc.
here's a patch to the top level Makefile to teach it about the shuffled files:


--- /local/caveh/linux/linux-2.6.31/Makefile    2009-09-09
15:13:59.000000000 -0700
+++ Makefile    2009-09-16 12:23:05.000000000 -0700
@@ -958,9 +958,9 @@ ifneq ($(KBUILD_SRC),)
                echo "  in the '$(srctree)' directory.";\
                /bin/false; \
        fi;
-       $(Q)if [ ! -d include2 ]; then                                  \
-           mkdir -p include2;                                          \
-           ln -fsn $(srctree)/include/asm-$(SRCARCH) include2/asm;     \
+       $(Q)if [ ! -d include2 ]; then                                   \
+           mkdir -p include2;                                           \
+           ln -fsn $(srctree)/arch/$(SRCARCH)/include/asm include2/asm; \
        fi
 endif