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 binutils-2.20.1.orig/bfd/elf64-ppc.c binutils-2.20.1/bfd/elf64-ppc.c

 --- binutils-2.20.1.orig/bfd/elf64-ppc.c	2010-02-03 14:28:25.000000000 +0100

 +++ binutils-2.20.1/bfd/elf64-ppc.c	2010-08-17 19:32:04.000000000 +0200

 @@ -11991,7 +11991,12 @@

  	      else if (!SYMBOL_REFERENCES_LOCAL (info, &h->elf)

  		       && !is_opd

  		       && r_type != R_PPC64_TOC)

 -		outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		{

 +		  outrel.r_info = ELF64_R_INFO (h->elf.dynindx, r_type);

 +		  if (h->elf.dynindx == -1

 +		      && h->elf.root.type == bfd_link_hash_undefweak)

 +		  memset (&outrel, 0, sizeof outrel);

 +		}

  	      else

  		{

  		  /* This symbol is local, or marked to become local,