Hash marks in Makefile need to be escaped [Bug #16935]

template/configure-ext.mk.tmpl

@@ -22,7 +22,7 @@ exts = {}
 end
 %>
 MINIRUBY = <%=miniruby%>
-SCRIPT_ARGS = <%=script_args%>
+SCRIPT_ARGS = <%=script_args.gsub("#", "\\#")%>
 EXTMK_ARGS = $(SCRIPT_ARGS) --gnumake=$(gnumake) --extflags="$(EXTLDFLAGS)" \
 	   --make-flags="MINIRUBY='$(MINIRUBY)'"