Set F as no-op and define __FlashStringHelper as char

Author: giulcioffi

Diff for: cores/arduino/Arduino.h

@@ -25,6 +25,10 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
 
+#undef F
+#define F(str) (str)
+#define __FlashStringHelper char
+
 #ifdef __cplusplus
 extern "C"{
 #endif