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>

 --- strace-orig/file.c	2008/05/20 04:56:18	1.92

 +++ strace/file.c	2008/08/01 01:13:10	1.93

 @@ -28,21 +28,22 @@

   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

   * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

   *

 - *	$Id: file.c,v 1.92 2008/05/20 04:56:18 roland Exp $

 + *	$Id: file.c,v 1.93 2008/08/01 01:13:10 roland Exp $

   */

  #include "defs.h"

  #include <dirent.h>

 +

  #ifdef LINUX

 -#define dirent kernel_dirent

 -#define dirent64 kernel_dirent64

 -#include <linux/types.h>

 -#include <linux/dirent.h>

 -#undef dirent

 -#undef dirent64

 +struct kernel_dirent {

 +	unsigned long   d_ino;

 +	unsigned long   d_off;

 +	unsigned short  d_reclen;

 +	char            d_name[1];

 +};

  #else

 -#define kernel_dirent dirent

 +# define kernel_dirent dirent

  #endif

  #ifdef LINUX