package/linuxptp: add patch to fix build failures with make 4.4

When using make 4.4 the KBOUD_OUTPUT environment variable provided to
the linuxptp makefile is not utilized. The added patch will fix that
behavior.

Fixes: http://autobuild.buildroot.net/results/5294fac7ed04945d47ea4eb2d1448bcbea5352bb/

Cc: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/linuxptp/0002-makefile-use-conditional-assignment-for-KBUILD_OUTPUT.patch

@@ -0,0 +1,43 @@
+From: Changqing Li <changqing.li@windriver.com>
+Date: Wed, 23 Nov 2022 08:23:46 +0800
+Subject: [Linuxptp-devel] [PATCH] makefile: use conditional assignment for KBUILD_OUTPUT
+
+Refer [1],from make 4.4, all variables that are marked as export will
+also be passed to the shell started by the shell function. use "=" will
+make KBUILD_OUTPUT always empty for shell function, use "?=" to make
+"export KBUILD_OUTPUT" in enrironment can work.
+
+[snip of 4.4 NEWS]
+* WARNING: Backward-incompatibility!
+   Previously makefile variables marked as export were not exported to commands
+   started by the $(shell ...) function.  Now, all exported variables are
+   exported to $(shell ...).
+[snip]
+
+[1] https://git.savannah.gnu.org/cgit/make.git/tree/NEWS?h=4.4&id=ed493f6c9116cc217b99c2cfa6a95f15803235a2#n74
+
+Signed-off-by: Changqing Li <changqing.li@windriver.com>
+
+[Retrieved from mailing list. The patch was not yet accepted and applied:
+https://www.mail-archive.com/linuxptp-devel@lists.sourceforge.net/msg06151.html]
+Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
+
+---
+ makefile | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/makefile b/makefile
+index 9aed383..ba3fb38 100644
+--- a/makefile
++++ b/makefile
+@@ -15,7 +15,7 @@
+ # with this program; if not, write to the Free Software Foundation, Inc.,
+ # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ 
+-KBUILD_OUTPUT =
++KBUILD_OUTPUT ?=
+ 
+ DEBUG	=
+ CC	= $(CROSS_COMPILE)gcc
+-- 
+2.25.1