Also parse -Dfoo in libtcc_test_mt

otherwise the -DTCC_ARM_VFP doesn't get through.

tests/libtcc_test_mt.c

@@ -108,7 +108,8 @@ void parse_args(TCCState *s)
                     *eq = 0;
                     tcc_define_symbol(s, a+2, eq+1);
                     *eq = '=';
-                }
+                } else
+                  tcc_define_symbol(s, a+2, NULL);
             }
         }
     }