/tmp/build6826651435799429866.tmp/GDBStub/GDBStub.c.o: In function `gdb_server':
/home/danny/src/sketchbook/esp8266/libraries/GDBStub/src/GDBStub.c:304: undefined reference to `uart_write_char_d'
collect2: error: ld returned 1 exit status
Error compiling.