Thanks, the last option is indeed the most convenient for me and works very well.
While I agree with you, I admit that there could be differing opinions.
$(eval $(call SetupHostCommand,which,Please install 'which', \
which which | grep which))
in some makefile(?). Not sure how that could be rewritten in a way to work reliably across distributions which all might have different declarations of which and without introducing new dependencies just to check for the build requirements.