add missing lib

lib/ArduinoJson/fuzzing/Makefile

@@ -0,0 +1,19 @@
+# CAUTION: this file is invoked by https://github.com/google/oss-fuzz
+
+CXXFLAGS += -I../src
+
+all: \
+	$(OUT)/json_fuzzer \
+	$(OUT)/json_fuzzer_seed_corpus.zip \
+	$(OUT)/json_fuzzer.options
+
+$(OUT)/json_fuzzer: fuzzer.cpp $(shell find ../src -type f)
+	$(CXX) $(CXXFLAGS) $< -o$@ $(LIB_FUZZING_ENGINE)
+
+$(OUT)/json_fuzzer_seed_corpus.zip: seed_corpus/*
+	zip -j $@ $?
+
+$(OUT)/json_fuzzer.options:
+	@echo "[libfuzzer]" > $@
+	@echo "max_len = 256" >> $@
+	@echo "timeout = 10" >> $@