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>

 ripped from Debian

  sysdeps/unix/sysv/linux/posix_fadvise.c |   13 +++++++++++++

  1 file changed, 13 insertions(+)

 diff -durN glibc-2.13.orig/sysdeps/unix/sysv/linux/posix_fadvise.c glibc-2.13/sysdeps/unix/sysv/linux/posix_fadvise.c

 --- glibc-2.13.orig/sysdeps/unix/sysv/linux/posix_fadvise.c	2003-08-17 02:36:22.000000000 +0200

 +++ glibc-2.13/sysdeps/unix/sysv/linux/posix_fadvise.c	2009-11-13 00:50:03.000000000 +0100

 @@ -35,6 +35,19 @@

      return INTERNAL_SYSCALL_ERRNO (ret, err);

    return 0;

  #else

 +# ifdef __NR_fadvise64_64

 +  INTERNAL_SYSCALL_DECL (err);  

 +  int ret = INTERNAL_SYSCALL (fadvise64_64, err, 6, fd,

 +			      __LONG_LONG_PAIR ((long) (offset >> 31),

 +						(long) offset),

 +			      __LONG_LONG_PAIR ((long) (len >> 31),

 +						(long) len),

 +			      advise);

 +  if (INTERNAL_SYSCALL_ERROR_P (ret, err))

 +    return INTERNAL_SYSCALL_ERRNO (ret, err);

 +  return 0;

 +# else

    return ENOSYS;

 +# endif

  #endif

  }