[PATCH net-next] tools: ynl: Fix out-of-tree build for ynltool

["Maxime Chevallier (Netdev Foundation)" <maxime.chevallier@bootlin.com>]

After the blamed commit, running a out-of-tree build for ynltool fails :

  # make -C tools/net/ynl/ynltool O=/tmp/o1
  make: Entering directory 'tools/net/ynl/ynltool'
  make: *** No rule to make target '/tmp/o1/json_writer.o', needed by '/tmp/o1/ynltool'.  Stop.

ynltool's Makefile correctly accounts for $(OUTPUT) to get the list of
object files to generate :

OBJS := $(patsubst %.c,$(OUTPUT)%.o,$(SRCS))

but it never actually set $(OUTPUT) before the blamed commit, meaning
that out-of-tree buils of ynltool were always actually in-tree.

Now, the O= parameter is correctly accounted for, and the %o: %c rule fails.

Let's update the %o: %c rule to also use $(OUTPUT).

Reported-by: Bobby Eshleman <bobbyeshleman@gmail.com>
Closes: https://lore.kernel.org/all/aqCyWQxqKDuQnZYR@devvm29614.prn0.facebook.com/
Fixes: 917f713b4ec4 ("tools: ynl: Allow cross-compiling ynl and associated tools")
Signed-off-by: Maxime Chevallier (Netdev Foundation) <maxime.chevallier@bootlin.com>
---
Targetting net-next, as the blamed commit lives there.

 tools/net/ynl/ynltool/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/net/ynl/ynltool/Makefile b/tools/net/ynl/ynltool/Makefile
index b8c67cdb4fdf..1053e7606c86 100644
--- a/tools/net/ynl/ynltool/Makefile
+++ b/tools/net/ynl/ynltool/Makefile
@@ -31,7 +31,7 @@ $(YNLTOOL): ../libynl.a $(OBJS)
 	$(Q)echo -e "\tLINK $@"
 	$(Q)$(CC) $(CFLAGS) -o $@ $(OBJS) ../libynl.a -lm
 
-%.o: %.c ../libynl.a
+$(OUTPUT)%.o: %.c ../libynl.a
 	$(Q)echo -e "\tCC $@"
 	$(Q)$(COMPILE.c) -MMD -c -o $@ $<
 
-- 
2.55.0