tools: ynl: build archives with $(AR)

Use $(AR) to allow build system to override the archiver tool (e.g.,
when cross-compiling for a different architecture) by setting the AR
environment variable.

GNU Make defaults AR to ar, so this change will not break existing build
environments that do not explicitly set AR.

Fixes: 07c3cc51a0 ("tools: net: package libynl for use in selftests")
Fixes: 86878f14d7 ("tools: ynl: user space helpers")
Signed-off-by: Greg Thelen <gthelen@google.com>
Link: https://patch.msgid.link/20260622161659.145047-1-gthelen@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/Makefile

@@ -22,7 +22,7 @@ tests: | lib generated libynl.a
 ynltool: | lib generated libynl.a
 libynl.a: | lib generated
 	@echo -e "\tAR $@"
-	@ar rcs $@ lib/ynl.o generated/*-user.o
+	@$(AR) rcs $@ lib/ynl.o generated/*-user.o
 
 $(SUBDIRS):
 	@if [ -f "$@/Makefile" ] ; then \

tools/net/ynl/generated/Makefile

@@ -37,7 +37,7 @@ all: protos.a $(HDRS) $(SRCS) $(KHDRS) $(KSRCS) $(UAPI) $(RSTS)
 
 protos.a: $(OBJS)
 	@echo -e "\tAR $@"
-	@ar rcs $@ $(OBJS)
+	@$(AR) rcs $@ $(OBJS)
 
 %-user.h: $(SPECS_DIR)/%.yaml $(TOOL)
 	@echo -e "\tGEN $@"

tools/net/ynl/lib/Makefile

@@ -15,7 +15,7 @@ all: ynl.a
 
 ynl.a: $(OBJS)
 	@echo -e "\tAR $@"
-	@ar rcs $@ $(OBJS)
+	@$(AR) rcs $@ $(OBJS)
 
 clean:
 	rm -f *.o *.d *~