utils/kamcmd: add missing USE_READLINE define for pkg-config build, related to #3284

(cherry picked from commit a70b6bf09c73d961ebea1947216757fafb951c24)

utils/kamcmd/Makefile

@@ -80,6 +80,7 @@ endif
 # detect libreadline
 ifneq ($(BUILDER),)
 	DEFS += $(shell $(BUILDER) --cflags readline)
+	DEFS+=-DUSE_READLINE
 	LIBS += $(shell $(BUILDER) --libs readline)
 	use_readline := 1
 else