Avoid isascii() & toascii() on Teensy 3.x too

teensy3/WCharacter.h

 // that fits into the ASCII character set.
 inline boolean isAscii(int c)
 {
-  return ( isascii (c) == 0 ? false : true);
+  return ((c & ~0x7F) != 0 ? false : true);
 }
 
 
 // ASCII character set, by clearing the high-order bits.
 inline int toAscii(int c)
 {
-  return toascii (c);
+  return (c & 0x7F);
 }