%B is not stripping the whole file extension

[uohmak4fvpqe]

I like to stack up extensions in each build step, so that I have, say, main.cc, then main.cc.o successive outputs. Which is why I actually didn't notice this before : %B seems to only strip the very last extension, for instance if in a rule %f is io.cc.o, then %B.so is io.cc.so, instead of io.so

I admit I'm not entirely sure however if that should be considered an issue or the expected behavior of %B. I feel like both could be useful, think about typical linux stuff like x.tar.xz.