Add basic support to semihosting #229

Job	Run time
Build Website	27s
Build Examples (espressif/esp)	2m 10s
Dry Run Packaging	1m 39s
Build Examples (gigadevice/gd32)	2m 10s
Check that stm32 generated code is up to date	39s
Build (ubuntu-latest)	33s
Build Examples (microchip/avr)	2m 16s
Build (windows-latest)	1m 14s
Build Examples (microchip/atsam)	1m 55s
Build (macos-latest)	30s
Unit Test Ports (ubuntu-latest, gigadevice/gd32)	15s
Build Examples (nordic/nrf5x)	2m 4s
Unit Test Regz (ubuntu-latest)	25s
Unit Test Ports (ubuntu-latest, raspberrypi/rp2xxx)	17s
Build Examples (nxp/lpc)	1m 56s
Unit Test Regz (windows-latest)	1m 9s
Unit Test Ports (ubuntu-latest, stmicro/stm32)	21s
Unit Test UF2 (ubuntu-latest)	16s
Unit Test Regz (macos-latest)	33s
Unit Test UF2 (windows-latest)	1m 39s
Build Examples (stmicro/stm32)	28s
Unit Test UF2 (macos-latest)	27s
Unit Test Ports (windows-latest, gigadevice/gd32)	2m 3s
Build Examples (raspberrypi/rp2xxx)	2m 24s
Unit Test Ports (windows-latest, raspberrypi/rp2xxx)	1m 53s
Build Examples (wch/ch32v)	2m 21s
Unit Test Ports (windows-latest, stmicro/stm32)	1m 4s
Unit Test Ports (macos-latest, gigadevice/gd32)	28s
Unit Test Ports (macos-latest, raspberrypi/rp2xxx)	33s
Unit Test Ports (macos-latest, stmicro/stm32)	38s
	34m 47s

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