Fix undefined behavior when printing INT_MIN/INT64_MIN.

Negating the most-negative signed integer results in overflow, which
is undefined behavior.  Fix this by casting to an unsigned type first
(unsigned overflow is well-defined as it uses modular arithmetic).

src/unity.c

@@ -183,7 +183,7 @@ void UnityPrintNumber(const UNITY_INT number_to_print)
     {
         /* A negative number, including MIN negative */
         UNITY_OUTPUT_CHAR('-');
-        number = (UNITY_UINT)(-number_to_print);
+        number = -number;
     }
     UnityPrintNumberUnsigned(number);
 }