add a make target for fuzz testing

Usage:

	$ make -f testing.mak fuzz
	Fuzz testing failure: lang: CSS input: Test/objectivec_property.h
	Fuzz testing failure: lang: Verilog input: Test/1880687.js
	Fuzz testing failure: lang: Verilog input: Test/jsFunc_tutorial.js
	Fuzz testing failure: lang: Vim input: Test/ocaml_empty.ml

Signed-off-by: Masatake YAMATO <yamato@redhat.com>