Add basic support to semihosting #203

Job	Run time
Build Website	22s
Dry Run Packaging	2m 19s
Build Examples (espressif/esp)	2m 7s
Build (ubuntu-latest)	32s
Build Examples (gigadevice/gd32)	2m 3s
Check that stm32 generated code is up to date	46s
Build (windows-latest)	1m 26s
Build Examples (microchip/avr)	2m 1s
Unit Test Ports (ubuntu-latest, gigadevice/gd32)	19s
Build (macos-latest)	37s
Build Examples (microchip/atsam)	2m 1s
Unit Test Ports (ubuntu-latest, raspberrypi/rp2xxx)	21s
Build Examples (nordic/nrf5x)	2m 0s
Unit Test Regz (ubuntu-latest)	17s
Unit Test Ports (ubuntu-latest, stmicro/stm32)	14s
Build Examples (nxp/lpc)	2m 5s
Unit Test Regz (windows-latest)	1m 12s
Unit Test UF2 (ubuntu-latest)	21s
Unit Test Ports (windows-latest, gigadevice/gd32)	59s
Build Examples (stmicro/stm32)	20s
Unit Test Regz (macos-latest)	52s
Unit Test UF2 (windows-latest)	59s
Unit Test Ports (windows-latest, raspberrypi/rp2xxx)	1m 1s
Build Examples (raspberrypi/rp2xxx)	2m 27s
Unit Test UF2 (macos-latest)	26s
Unit Test Ports (windows-latest, stmicro/stm32)	1m 9s
Build Examples (wch/ch32v)	2m 5s
Unit Test Ports (macos-latest, gigadevice/gd32)	35s
Unit Test Ports (macos-latest, raspberrypi/rp2xxx)	56s
Unit Test Ports (macos-latest, stmicro/stm32)	38s
	33m 30s

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