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 -urN uClibc-dist/libc/sysdeps/linux/common/bits/uClibc_touplow.h uClibc/libc/sysdeps/linux/common/bits/uClibc_touplow.h

 --- uClibc-dist/libc/sysdeps/linux/common/bits/uClibc_touplow.h   Fri Jun  3 13:30:25 2005

 +++ uClibc/libc/sysdeps/linux/common/bits/uClibc_touplow.h   Fri Jun  3 13:30:39 2005

 @@ -34,11 +34,11 @@

  /* glibc uses the equivalent of - typedef __int32_t __ctype_touplow_t; */

 -typedef __uint16_t __ctype_mask_t;

 +typedef __uint32_t __ctype_mask_t;

  #ifdef __UCLIBC_HAS_CTYPE_SIGNED__

 -typedef __int16_t __ctype_touplow_t;

 +typedef __int32_t __ctype_touplow_t;

  #define __UCLIBC_CTYPE_B_TBL_OFFSET       128

  #define __UCLIBC_CTYPE_TO_TBL_OFFSET      128