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 -dur libelf-0.8.10.orig/configure libelf-0.8.10/configure

--- libelf-0.8.10.orig/configure	2007-09-07 14:08:06.000000000 +0200

+++ libelf-0.8.10/configure	2008-10-23 22:43:19.000000000 +0200

@@ -1595,7 +1595,7 @@

   echo $ac_n "(cached) $ac_c" 1>&6

 else

   if test "$cross_compiling" = yes; then

-  ac_cv_sizeof_long_long=0

+  ac_cv_sizeof_long_long=8

 else

   cat > conftest.$ac_ext <<EOF

 #line 1602 "configure"

diff -dur libelf-0.8.10.orig/configure.in libelf-0.8.10/configure.in

--- libelf-0.8.10.orig/configure.in	2007-09-07 14:07:59.000000000 +0200

+++ libelf-0.8.10/configure.in	2008-10-23 22:43:10.000000000 +0200

@@ -90,7 +90,7 @@

 AC_CHECK_SIZEOF(short,2)

 AC_CHECK_SIZEOF(int,4)

 AC_CHECK_SIZEOF(long,4)

-AC_CHECK_SIZEOF(long long,0)

+AC_CHECK_SIZEOF(long long,8)

 # Windows port

 AC_CHECK_SIZEOF(__int64, 0)