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>

From: http://sourceware.org/ml/crossgcc/2008-10/msg00044.html

From: http://sources.redhat.com/ml/libc-ports/2007-06/msg00005.html

2007-06-07  Steven Munroe  <sjmunroe@us.ibm.com>

    * sysdeps/powerpc/nofpu/Makefile: Remove fe_nomask from libm-support.

diff -urN glibc-2.6.orig/glibc-ports-2.6.1/sysdeps/powerpc/nofpu/Makefile glibc-2.6/glibc-ports-2.6.1/sysdeps/powerpc/nofpu/Makefile

--- glibc-2.6.orig/glibc-ports-2.6.1/sysdeps/powerpc/nofpu/Makefile	2006-11-22 09:13:11.000000000 -0600

+++ glibc-2.6/glibc-ports-2.6.1/sysdeps/powerpc/nofpu/Makefile	2007-06-07 09:53:05.708240976 -0500

@@ -6,7 +6,7 @@

 endif

 ifeq ($(subdir),math)

-libm-support += fenv_const fe_nomask

+libm-support += fenv_const

 CPPFLAGS += -I../soft-fp/

 # The follow CFLAGS are a work around for GCC Bugzilla Bug 29253

 # "expand_abs wrong default code for floating point"