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>

 Original patch from: gentoo/src/patchsets/glibc/2.9/1018_all_glibc-awk-in-C-locale.patch

 -= BEGIN original header =-

 http://bugs.gentoo.org/252802

 2008-12-29  Mike Frysinger  <vapier@gentoo.org>

 	* iconvdata/Makefile (iconv-rules): Use LC_ALL=C when running awk script.

 -= END original header =-

 diff -durN glibc-2_9.orig/iconvdata/Makefile glibc-2_9/iconvdata/Makefile

 --- glibc-2_9.orig/iconvdata/Makefile	2008-05-15 03:54:31.000000000 +0200

 +++ glibc-2_9/iconvdata/Makefile	2009-02-02 22:00:50.000000000 +0100

 @@ -286,7 +286,7 @@

  	{ echo $(filter-out lib%, $(modules)); \

  	  echo 8bit $(gen-8bit-modules); \

  	  echo 8bit-gap $(gen-8bit-gap-modules); } | \

 -	$(AWK) 'NR == 1 { \

 +	LC_ALL=C $(AWK) 'NR == 1 { \

  		  for (i = 1; i <= NF; i++) { \

  		    printf "%s-routines := %s\n", $$i, tolower($$i); \

  		    printf "%s-map := gconv.map\n", $$i; \