fix: prevent unused warning

When NDEBUG is defined and the _Error_Handler() is used
inside a function using function arguments.

Ex:
void dummy(char *file, uint32_t line) {
  _Error_Handler(file, line);
}

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

cores/arduino/stm32/stm32_def.h

@@ -133,6 +133,8 @@ void SystemClock_Config(void);
 #if !defined(_Error_Handler)
 #define _Error_Handler(str, value) \
   while (1) {\
+    (void)str;\
+    (void)value;\
   }
 #endif
 #if !defined(Error_Handler)