Add basic support to semihosting #233

Job	Run time
Build (ubuntu-latest)	32s
Dry Run Packaging	1m 55s
Build (windows-latest)	1m 41s
Build Website	21s
Build Examples (espressif/esp)	2m 10s
Build (macos-latest)	27s
Build Examples (gigadevice/gd32)	2m 9s
Check that stm32 generated code is up to date	45s
Build Examples (microchip/avr)	2m 18s
Build Examples (microchip/atsam)	2m 3s
Unit Test Regz (ubuntu-latest)	20s
Build Examples (nordic/nrf5x)	2m 2s
Unit Test Ports (ubuntu-latest, gigadevice/gd32)	14s
Unit Test Regz (windows-latest)	1m 28s
Unit Test UF2 (ubuntu-latest)	22s
Build Examples (nxp/lpc)	2m 0s
Unit Test Regz (macos-latest)	30s
Unit Test Ports (ubuntu-latest, raspberrypi/rp2xxx)	17s
Unit Test UF2 (windows-latest)	1m 18s
Build Examples (stmicro/stm32)	31s
Unit Test UF2 (macos-latest)	35s
Unit Test Ports (ubuntu-latest, stmicro/stm32)	27s
Build Examples (raspberrypi/rp2xxx)	2m 24s
Unit Test Ports (windows-latest, gigadevice/gd32)	1m 13s
Build Examples (wch/ch32v)	2m 13s
Unit Test Ports (windows-latest, raspberrypi/rp2xxx)	56s
Unit Test Ports (windows-latest, stmicro/stm32)	1m 29s
Unit Test Ports (macos-latest, gigadevice/gd32)	31s
Unit Test Ports (macos-latest, raspberrypi/rp2xxx)	36s
Unit Test Ports (macos-latest, stmicro/stm32)	37s
	34m 24s

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