kernel/linux: fix using custom location

Currently, extract and patch are skipped as thus:
- using a custom directory of pre-installed headers
- a correctly named directory already exists

Otherwise, extract and patch are done.

The current second condition is wrong, because it allows the following
sequence to happen:
- a non-custom kernel is used
- a previous build only partially extracted the non-custom sources
- that p[revious build broke during extraction (eg. incomplete tarball...)
- a subsequent build will find a properly named directory, and will
thus skip extract and patch, which is wrong

Fix that by following the conditions in this table:

Type | Extract | Patch
----------------------+---------+-------
Pre-installed headers | N | N
custom directory | N | N
custom tarball | Y | N
mainstream tarball | Y | Y

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: David Holsgrove <david.holsgrove@xilinx.com>

diff -durN gcc-3.4.6.orig/gcc/config/rs6000/linux-unwind.h gcc-3.4.6/gcc/config/rs6000/linux-unwind.h

--- gcc-3.4.6.orig/gcc/config/rs6000/linux-unwind.h	2005-03-17 11:41:18.000000000 +0100

+++ gcc-3.4.6/gcc/config/rs6000/linux-unwind.h	2007-08-15 23:07:00.000000000 +0200

@@ -32,6 +32,7 @@

    these structs elsewhere;  Many fields are missing, particularly

    from the end of the structures.  */

+#ifndef inhibit_libc

 struct gcc_vregs

 {

   __attribute__ ((vector_size (16))) int vr[32];

@@ -320,3 +321,4 @@

 									\

     goto SUCCESS;							\

   } while (0)

+#endif