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 glibc-ports-2.7.orig/sysdeps/unix/sysv/linux/arm/ioperm.c glibc-ports-2.7/sysdeps/unix/sysv/linux/arm/ioperm.c

 --- glibc-2.7.orig/glibc-ports-2.7/sysdeps/unix/sysv/linux/arm/ioperm.c	2005-06-10 13:12:09.000000000 +0200

 +++ glibc-2.7/glibc-ports-2.7/sysdeps/unix/sysv/linux/arm/ioperm.c	2008-05-18 16:19:45.000000000 +0200

 @@ -45,7 +45,6 @@

  #include <sys/mman.h>

  #include <linux/version.h>

 -#include <asm/page.h>

  #include <sys/sysctl.h>

  #define PATH_ARM_SYSTYPE	"/etc/arm_systype"