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 gcc-3.4.6.orig/gcc/config/sh/lib1funcs.asm gcc-3.4.6/gcc/config/sh/lib1funcs.asm

 --- gcc-3.4.6.orig/gcc/config/sh/lib1funcs.asm	2003-08-12 03:25:07.000000000 +0200

 +++ gcc-3.4.6/gcc/config/sh/lib1funcs.asm	2007-08-15 23:04:26.000000000 +0200

 @@ -37,9 +37,19 @@

     ELF local label prefixes by J"orn Rennecke

     amylaar@cygnus.com  */

 +#define ALIAS(X,Y)	.global GLOBAL(X); .set GLOBAL(X),GLOBAL(Y)

 +

  #ifdef __ELF__

  #define LOCAL(X)	.L_##X

 -#define FUNC(X)		.type X,@function

 +

 +#if 1 /* ??? The export list mechanism is broken, everything that is not

 +	 hidden is exported.  */

 +#undef FUNC

 +#define FUNC(X)		.type X,@function; .hidden X

 +#undef ALIAS

 +#define ALIAS(X,Y)	.global GLOBAL(X); .set GLOBAL(X),GLOBAL(Y); .hidden GLOBAL(X)

 +#endif

 +

  #define ENDFUNC0(X)	.Lfe_##X: .size X,.Lfe_##X-X

  #define ENDFUNC(X)	ENDFUNC0(X)

  #else