Add msp430 gcc9 to build matrix #19

Job	Run time
call-compile-sketches-workflow (msp, energia:msp430:MSP-EXP430G2553LP, energia:msp430, https://ra... / compile-sketches	41s
call-compile-sketches-workflow (esp8266, esp8266:esp8266:thing, esp8266:esp8266, http://arduino.e... / compile-sketches	46s
call-compile-sketches-workflow (esp32, esp32:esp32:esp32, esp32:esp32, https://espressif.github.i... / compile-sketches	1m 26s
call-compile-sketches-workflow (stm32, STMicroelectronics:stm32:GenF1:pnum=BLUEPILL_F103C8, STMic... / compile-sketches	1m 17s
call-compile-sketches-workflow (msp-gcc9, energia:msp430gcc9:MSP-EXP430G2553LP, energia:msp430gcc... / compile-sketches	44s
call-compile-sketches-workflow (avr, arduino:avr:uno, arduino:avr, https://downloads.arduino.cc/p... / compile-sketches	40s
	5m 34s

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