The issue with these "; @:" thinglets is that mkimage-profiles
relies on target tracing (see commit 788cad88 some four years ago);
and this tracing approach relies on non-empty recipes which do call
shell (which gets (ab)used) unlike empty ones which oviously don't.

So this _will_ be traced properly:

    a: b
	@echo "hello world"

and this will too:

    a: b; @:

but this will result in a broken graph with REPORT=1:

    a: b