Added debugging compiler flag

Makefile

@@ -6,6 +6,8 @@ SOURCES := ast.ml lexer.mll parser.mly util.mli util.ml stringify.mli \
 PRE_TARGETS := ast.cmi
 LIBS := str
 
+OCAMLFLAGS := -g
+
 OCAMLYACC := menhir
 YFLAGS := --infer