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 glibc-2.6.1.orig/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h glibc-2.6.1/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h

 --- glibc-2.6.1.orig/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h	2005-11-16 20:22:59.000000000 +0100

 +++ glibc-2.6.1/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h	2007-09-06 13:53:16.000000000 +0200

 @@ -126,3 +126,9 @@

  # define NO_CANCELLATION 1

  #endif

 +

 +#ifndef __ASSEMBLER__

 +# define RTLD_SINGLE_THREAD_P \

 +  __builtin_expect (THREAD_GETMEM (THREAD_SELF, \

 +                   header.multiple_threads) == 0, 1)

 +#endif