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/gcc/config.gcc.uclibc100-sh~	2006-03-06 20:46:56 +0100

 +++ gcc/gcc/config.gcc	2006-03-10 15:02:41 +0100

 @@ -1905,7 +1905,7 @@

  	;;

  sh-*-elf* | sh[12346l]*-*-elf* | sh*-*-kaos* | \

  sh-*-symbianelf* | sh[12346l]*-*-symbianelf* | \

 -  sh-*-linux* | sh[346lbe]*-*-linux* | \

 +  sh*-*-linux* | sh[346lbe]*-*-linux* | \

    sh-*-netbsdelf* | shl*-*-netbsdelf* | sh5-*-netbsd* | sh5l*-*-netbsd* | \

     sh64-*-netbsd* | sh64l*-*-netbsd*)

  	tmake_file="${tmake_file} sh/t-sh sh/t-elf"