use the standalone runner when LIB_FUZZING_ENGINE is not set

fuzz/CMakeLists.txt

@@ -7,10 +7,25 @@ include_directories(PUBLIC ${CMAKE_SOURCE_DIR})
 foreach(FUZZERNAME
 	tokener_parse_ex_fuzzer)
 
-add_executable(${FUZZERNAME} ${FUZZERNAME}.cc standalone_runner.cc)
+	add_executable(${FUZZERNAME}
+		${FUZZERNAME}.cc)
 
-target_include_directories(${FUZZERNAME} PUBLIC ${PROJECT_BINARY_DIR})
+	target_include_directories(${FUZZERNAME}
+		PUBLIC
+		${PROJECT_BINARY_DIR})
 
-target_link_libraries(${FUZZERNAME} PRIVATE json-c)
+	set_target_properties(${FUZZERNAME} PROPERTIES CXX_STANDARD 11)
 
+	# define whether we want to use the standalone runner for our own testing or
+	# link against libFuzzer populated from env variables
+	if (NOT DEFINED $ENV{LIB_FUZZING_ENGINE})
+		add_library(standalone_runner standalone_runner.cc)
+		target_link_libraries(${FUZZERNAME}
+			json-c
+			standalone_runner)
+	else()
+		target_link_libraries(${FUZZERNAME}
+			json-c
+			${LIB_FUZZING_ENGINE})
+	endif()
 endforeach(FUZZERNAME)