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>

 --- a/bfd/elf32-arm.c

 +++ b/bfd/elf32-arm.c

 @@ -12408,7 +12408,8 @@ elf32_arm_check_relocs (bfd *abfd, struc

  	  /* If the symbol is a function that doesn't bind locally,

  	     this relocation will need a PLT entry.  */

 -	  root_plt->refcount += 1;

 +	  if (root_plt->refcount != -1)

 +	    root_plt->refcount += 1;

  	  if (!call_reloc_p)

  	    arm_plt->noncall_refcount++;