Add Arduino M0 Pro support

[gandarez]

This is an ongoing PR.

It was heavily based on boards.txt from Arduino repo.

It fails to build with:

tinygo flash -target arduino-m0-pro ./main.go Avrdude version 8.0 Copyright see https://github.com/avrdudes/avrdude/blob/main/AUTHORS System wide configuration file is /opt/homebrew/etc/avrdude.conf User configuration file <User>/.avrduderc does not exist Warning: system wide configuration file version (7.3) does not match Avrdude build version (8.0) Using port : /dev/cu.usbmodem004F1 Using programmer : stk500v2 Setting baud rate : 57600 AVR part : ATmega2560 Programming modes : SPM, ISP, HVPP, JTAG Programmer type : STK500V2 Description : Atmel STK500 version 2.x firmware Programmer model : AVRISP HW version : 3 FW Version Controller : 4.05 Vtarget : 0.0 V SCK period : 0.1 us AVR device initialized and ready to accept instructions Device signature = 1E 98 01 (ATmega2560) Auto-erasing chip as flash memory needs programming (-U flash:w:...) specify the -D option to disable this feature Erased chip Reading 6184 bytes for flash from input file main.hex in 1 section [0x2000, 0x3827]: 25 pages and 216 pad bytes Writing 6184 bytes to flash Writing | ################################################## | 100% 0.21 s Reading | ################################################## | 100% 0.18 s Warning: flash verification mismatch device 0xff != input 0x00 at addr 0x2000 (error) device 0xff != input 0x08 at addr 0x2001 (error) device 0xff != input 0x00 at addr 0x2002 (error) device 0xff != input 0x20 at addr 0x2003 (error) device 0xff != input 0x19 at addr 0x2004 (error) device 0xff != input 0x32 at addr 0x2005 (error) device 0xff != input 0x00 at addr 0x2006 (error) device 0xff != input 0x00 at addr 0x2007 (error) device 0xff != input 0x37 at addr 0x2008 (error) device 0xff != input 0x21 at addr 0x2009 (error) suppressing further verification errors Error: flash verification mismatch Avrdude done. Thank you. failed to flash /var/folders/m4/q3fvlgld52d2m3k1wmmvb1pm0000gn/T/tinygo2035335312/main.hex: exit status 1