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-0.9.33.2~orig/Rules.mak uClibc-0.9.33.2/Rules.mak

--- uClibc-0.9.33.2~orig/Rules.mak	2012-05-15 09:20:09.000000000 +0200

+++ uClibc-0.9.33.2/Rules.mak	2012-09-24 14:09:51.092953729 +0200

@@ -226,6 +226,7 @@

 OPTIMIZATION:=

 # Use '-Os' optimization if available, else use -O2, allow Config to override

+ifneq ($(TARGET_ARCH),m68k)

 $(eval $(call check-gcc-var,-Os))

 ifneq ($(CFLAG_-Os),)

 OPTIMIZATION += $(CFLAG_-Os)

@@ -233,6 +234,7 @@

 $(eval $(call check-gcc-var,-O2))

 OPTIMIZATION += $(CFLAG_-O2)

 endif

+endif

 # Use the gcc 3.4 -funit-at-a-time optimization when available

 $(eval $(call check-gcc-var,-funit-at-a-time))

 OPTIMIZATION += $(CFLAG_-funit-at-a-time)