Compatibility with libraries that include only Print.h

teensy3/WString.h

 #include <ctype.h>
 #include "avr_functions.h"
 
+// Not needed here, but some libs assume WString.h or Print.h
+// gives them PROGMEM and other AVR stuff.
+#include "avr/pgmspace.h"
+
 // When compiling programs with this class, the following gcc parameters
 // dramatically increase performance and memory (RAM) efficiency, typically
 // with little or no increase in code size.