Added a compatibility trick in `debug -I` for `toolchain.prefix` key #3856

Job	Run time
run-determination	1s
check-formatting (./)	10s
check-outdated (./)	10s
build (arduino/discovery/discovery_client)	41s
check-config (./)	9s
build (client_example)	27s
check-license-headers (./)	13s
build (commands/daemon/term_example)	27s
check-style (./)	36s
	2m 54s

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