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>

 Original patch from gentoo: gentoo/src/patchsets/gcc/4.3.1/gentoo/66_all_gcc43-pr25343.patch

 http://gcc.gnu.org/PR25343

 sniped from Debian

 2008-04-27  Roman Zippel <zippel@linux-m68k.org>

 	* config/host-linux.c (TRY_EMPTY_VM_SPACE): Define for __mc68000__.

 diff -durN gcc-4.3.1.orig/gcc/config/host-linux.c gcc-4.3.1/gcc/config/host-linux.c

 --- gcc-4.3.1.orig/gcc/config/host-linux.c	2007-08-02 12:49:31.000000000 +0200

 +++ gcc-4.3.1/gcc/config/host-linux.c	2008-06-10 14:58:28.000000000 +0200

 @@ -84,6 +84,8 @@

  # define TRY_EMPTY_VM_SPACE	0x8000000000

  #elif defined(__sparc__)

  # define TRY_EMPTY_VM_SPACE	0x60000000

 +#elif defined(__mc68000__)

 +# define TRY_EMPTY_VM_SPACE	0x40000000

  #else

  # define TRY_EMPTY_VM_SPACE	0

  #endif