Only define BYTE (ancient Arduino) if not conflicting with other headers

teensy/Print.h

 #define HEX 16
 #define OCT 8
 #define BIN 2
+
+// BYTE was defined in very old versions of Arduino
+// maybe this now causes more trouble than it's worth?
+#ifndef BYTE
 #define BYTE 0
+#endif
 
 class __FlashStringHelper;
 

teensy3/Print.h

 #define HEX 16
 #define OCT 8
 #define BIN 2
+
+// BYTE was defined in very old versions of Arduino
+// maybe this now causes more trouble than it's worth?
+#ifndef BYTE
 #define BYTE 0
+#endif
 
 class __FlashStringHelper;