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 glibc-2.10.1.orig/sysdeps/sh/sh4/fpu/fpu_control.h glibc-2.10.1/sysdeps/sh/sh4/fpu/fpu_control.h

 --- glibc-2.10.1.orig/sysdeps/sh/sh4/fpu/fpu_control.h	2001-07-06 06:56:04.000000000 +0200

 +++ glibc-2.10.1/sysdeps/sh/sh4/fpu/fpu_control.h	2009-11-13 00:51:26.000000000 +0100

 @@ -45,6 +45,7 @@

  #define _FPU_GETCW(cw) __asm__ ("sts fpscr,%0" : "=r" (cw))

  #if defined __GNUC__

 +extern void __set_fpscr(unsigned long);

  #define _FPU_SETCW(cw) __set_fpscr ((cw))

  #else

  #define _FPU_SETCW(cw) __asm__ ("lds %0,fpscr" : : "r" (cw))