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 ltrace-0.5.2.orig/configure ltrace-0.5.2/configure

--- ltrace-0.5.2.orig/configure	2009-09-14 18:47:45.000000000 +0200

+++ ltrace-0.5.2/configure	2009-09-14 18:49:18.000000000 +0200

@@ -1829,6 +1829,9 @@

   linux-gnu*) host_os=linux-gnu

 esac

 HOST_OS="$host_os"

+case "${HOST_OS}" in

+  linux-*) HOST_OS=linux-gnu;;

+esac

 ac_ext=c

diff -durN ltrace-0.5.2.orig/configure.ac ltrace-0.5.2/configure.ac

--- ltrace-0.5.2.orig/configure.ac	2009-09-14 18:47:45.000000000 +0200

+++ ltrace-0.5.2/configure.ac	2009-09-14 18:49:18.000000000 +0200

@@ -10,6 +10,9 @@

   linux-gnu*) host_os=linux-gnu

 esac

 HOST_OS="$host_os"

+case "${HOST_OS}" in

+  linux-*) HOST_OS=linux-gnu;;

+esac

 AC_SUBST(HOST_OS)

 HOST_ARCH="$host_cpu"

 AC_SUBST(HOST_ARCH)