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>

 --- ppl-0.10.2/configure.orig	2010-08-04 21:48:19.000000000 -0400

 +++ ppl-0.10.2/configure	2010-08-04 21:50:04.000000000 -0400

 @@ -16443,6 +16443,10 @@

  #GMP version 4.1.3 or higher is required

  #endif

 +#ifndef BITS_PER_MP_LIMB

 +#define BITS_PER_MP_LIMB GMP_LIMB_BITS

 +#endif

 +

  int

  main() {

    std::string header_version;

 @@ -16469,11 +16473,11 @@

      return 1;

    }

 -  if (sizeof(mp_limb_t)*CHAR_BIT != GMP_LIMB_BITS

 -      || GMP_LIMB_BITS != mp_bits_per_limb) {

 +  if (sizeof(mp_limb_t)*CHAR_BIT != BITS_PER_MP_LIMB

 +      || BITS_PER_MP_LIMB != mp_bits_per_limb) {

      std::cerr

        << "GMP header (gmp.h) and library (ligmp.*) bits-per-limb mismatch:\n"

 -      << "header gives " << __GMP_BITS_PER_MP_LIMB << ";\n"

 +      << "header gives " << BITS_PER_MP_LIMB << ";\n"

        << "library gives " << mp_bits_per_limb << ".\n"

        << "This probably means you are on a bi-arch system and\n"

        << "you are compiling with the wrong header or linking with\n"