Arduino: 1.8.4 (Windows 10), TD: 1.38, Board: "Teensy 3.6, Serial, 180 MHz, Faster, US English"
...
Linking everything together...
"D:\arduino-1.8.4\hardware\teensy/../tools/arm/bin/arm-none-eabi-gcc" -O2 -Wl,--gc-sections,--relax,--defsym=__rtc_localtime=1503989929 "-TD:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/mk66fx1m0.ld" -lstdc++ -mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsingle-precision-constant -o "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766/xxx.ino.elf" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\sketch\xxx.ino.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\enumeration.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\hub.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\keyboard.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\memory.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\midi.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\mouse.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\print.cpp.o" "C:\Users\kurte\AppData\Local\Temp\arduino_build_229766/core\core.a" "-LC:\Users\kurte\AppData\Local\Temp\arduino_build_229766" -larm_cortexM4lf_math -lm
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `usb_serial_class::write(unsigned char const*, unsigned int)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/usb_serial.h:95: undefined reference to `usb_serial_write'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `Print::print(unsigned long)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/Print.h:68: undefined reference to `Print::printNumber(unsigned long, unsigned char, unsigned char)'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `usb_serial_class::write(unsigned char const*, unsigned int)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/usb_serial.h:95: undefined reference to `usb_serial_write'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `Print::print(unsigned long, int)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/Print.h:74: undefined reference to `Print::printNumber(unsigned long, unsigned char, unsigned char)'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `usb_serial_class::write(unsigned char const*, unsigned int)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/usb_serial.h:95: undefined reference to `usb_serial_write'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\ehci.cpp.o: In function `Print::print(unsigned long, int)':
...
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/Print.h:70: undefined reference to `Print::printNumber(unsigned long, unsigned char, unsigned char)'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\print.cpp.o: In function `usb_serial_class::write(unsigned char)':
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/usb_serial.h:94: undefined reference to `usb_serial_putchar'
D:\arduino-1.8.4\hardware\teensy\avr\cores\teensy3/usb_serial.h:94: undefined reference to `usb_serial_putchar'
C:\Users\kurte\AppData\Local\Temp\arduino_build_229766\libraries\USBHost_t36\print.cpp.o: In function `USBHost::print_hexbytes(void const*, unsigned long)':
C:\Users\kurte\Documents\Arduino\libraries\USBHost_t36/print.cpp:184: undefined reference to `Serial'
C:\Users\kurte\Documents\Arduino\libraries\USBHost_t36/print.cpp:184: undefined reference to `Print::println()'
collect2.exe: error: ld returned 1 exit status
Multiple libraries were found for "USBHost_t36.h"
Used: C:\Users\kurte\Documents\Arduino\libraries\USBHost_t36
Not used: D:\arduino-1.8.4\hardware\teensy\avr\libraries\USBHost_t36
Using library USBHost_t36 at version 0.1 in folder: C:\Users\kurte\Documents\Arduino\libraries\USBHost_t36
Error compiling for board Teensy 3.6.