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-2.21.1.orig/ld/emultempl/elf32.em binutils-2.21.1/ld/emultempl/elf32.em

--- binutils-2.21.1.orig/ld/emultempl/elf32.em	2011-06-27 09:39:14.000000000 +0200

+++ binutils-2.21.1/ld/emultempl/elf32.em	2011-09-12 13:39:08.808908274 +0200

@@ -1272,6 +1272,8 @@

 	      && command_line.rpath == NULL)

 	    {

 	      lib_path = (const char *) getenv ("LD_RUN_PATH");

+	      if ((lib_path) && (strlen (lib_path) == 0))

+	      	lib_path = NULL;

 	      if (gld${EMULATION_NAME}_search_needed (lib_path, &n,

 						      force))

 		break;

@@ -1499,6 +1501,8 @@

   rpath = command_line.rpath;

   if (rpath == NULL)

     rpath = (const char *) getenv ("LD_RUN_PATH");

+  if ((rpath) && (strlen (rpath) == 0))

+  	rpath = NULL;

   for (abfd = link_info.input_bfds; abfd; abfd = abfd->link_next)

     if (bfd_get_flavour (abfd) == bfd_target_elf_flavour)