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-4.5.2.orig/libjava/Makefile.in gcc-4.5.2/libjava/Makefile.in

 --- gcc-4.5.2.orig/libjava/Makefile.in	2010-12-16 13:49:03.000000000 +0100

 +++ gcc-4.5.2/libjava/Makefile.in	2010-12-29 23:02:41.000000000 +0100

 @@ -9463,6 +9463,9 @@

  ecjx$(EXEEXT): $(ecjx_OBJECTS) $(ecjx_DEPENDENCIES) 

  	@rm -f ecjx$(EXEEXT)

  	$(ecjx_LINK) $(ecjx_OBJECTS) $(ecjx_LDADD) $(LIBS)

 +ecjx.$(OBJEXT): $(ecjx_SOURCES)

 +	@rm -f ecjx.$(OBJEXT)

 +	$(CC_FOR_BUILD) $(BUILD_CFLAGS) -c -o $@ $<

  gappletviewer$(EXEEXT): $(gappletviewer_OBJECTS) $(gappletviewer_DEPENDENCIES) 

  	@rm -f gappletviewer$(EXEEXT)

  	$(gappletviewer_LINK) $(gappletviewer_OBJECTS) $(gappletviewer_LDADD) $(LIBS)