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>

--- gcc-4.1.0/libstdc++-v3/include/ext/rope.mps	2006-03-24 01:49:51 +0100

+++ gcc-4.1.0/libstdc++-v3/include/ext/rope	2006-03-24 01:49:37 +0100

@@ -59,6 +59,9 @@

 #include <bits/allocator.h>

 #include <ext/hash_fun.h>

+/* cope w/ index defined as macro, SuSv3 proposal */

+#undef index

+

 # ifdef __GC

 #   define __GC_CONST const

 # else

--- gcc-4.1.0/libstdc++-v3/include/ext/ropeimpl.h.mps	2006-03-24 01:50:04 +0100

+++ gcc-4.1.0/libstdc++-v3/include/ext/ropeimpl.h	2006-03-24 01:50:28 +0100

@@ -53,6 +53,9 @@

 #include <ext/memory> // For uninitialized_copy_n

 #include <ext/numeric> // For power

+/* cope w/ index defined as macro, SuSv3 proposal */

+#undef index

+

 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)

   using std::size_t;