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>

http://sources.redhat.com/ml/binutils/2004-04/msg00665.html

fixes building on some architectures (like m68k/arm/cris/etc...) because

it does the right thing

diff -durN glibc-2.12.1.orig/include/libc-symbols.h glibc-2.12.1/include/libc-symbols.h

--- glibc-2.12.1.orig/include/libc-symbols.h	2009-03-14 00:51:46.000000000 +0100

+++ glibc-2.12.1/include/libc-symbols.h	2009-11-13 00:50:07.000000000 +0100

@@ -239,12 +239,12 @@

 #  define __make_section_unallocated(section_string)

 # endif

-/* Tacking on "\n\t#" to the section name makes gcc put it's bogus

+/* Tacking on "\n#APP\n\t#" to the section name makes gcc put it's bogus

    section attributes on what looks like a comment to the assembler.  */

 # ifdef HAVE_SECTION_QUOTES

-#  define __sec_comment "\"\n\t#\""

+#  define __sec_comment "\"\n#APP\n\t#\""

 # else

-#  define __sec_comment "\n\t#"

+#  define __sec_comment "\n#APP\n\t#"

 # endif

 # define link_warning(symbol, msg) \

   __make_section_unallocated (".gnu.warning." #symbol) \