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 strace-4.5.16.orig/configure.ac strace-4.5.16/configure.ac

 --- strace-4.5.16.orig/configure.ac	2007-07-14 19:25:25.000000000 +0200

 +++ strace-4.5.16/configure.ac	2007-07-14 19:27:35.000000000 +0200

 @@ -91,14 +91,14 @@

  	arch=hppa

  	AC_DEFINE([HPPA], 1, [Define for the HPPA architecture.])

  	;;

 -sh)

 -	arch=sh

 -	AC_DEFINE([SH], 1, [Define for the SH architecture.])

 -	;;

  sh64)

  	arch=sh64

  	AC_DEFINE([SH64], 1, [Define for the SH64 architecture.])

  	;;

 +sh*)

 +	arch=sh

 +	AC_DEFINE([SH], 1, [Define for the SH architecture.])

 +	;;

  x86?64*)

  	arch=x86_64

  	AC_DEFINE([X86_64], 1, [Define for the AMD x86-64 architecture.])