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>

 On 20081011, Khem RAJ writes:

  You have to bar gcc trying to build unwinding at stage 1. Try the

  attached patch and see if it helps.

  gcc/config/sh/linux-unwind.h |    3 +++

  1 file changed, 3 insertions(+)

 Index: gcc-4_2-branch/gcc/config/sh/linux-unwind.h

 ===================================================================

 --- gcc-4_2-branch.orig/gcc/config/sh/linux-unwind.h	2008-07-01 17:24:40.000000000 -0700

 +++ gcc-4_2-branch/gcc/config/sh/linux-unwind.h	2008-07-01 17:25:47.000000000 -0700

 @@ -26,6 +26,8 @@ along with this program; see the file CO

  the Free Software Foundation, 51 Franklin Street, Fifth Floor,

  Boston, MA 02110-1301, USA.  */

 +#ifndef inhibit_libc

 +

  /* Do code reading to identify a signal frame, and set the frame

     state data appropriately.  See unwind-dw2.c for the structs.  */

 @@ -251,3 +253,4 @@ sh_fallback_frame_state (struct _Unwind_

    return _URC_NO_REASON;

  }

  #endif /* defined (__SH5__) */

 +#endif /* ifndef inhibit_libc */