Hi,

yesterday I noticed that, as I vaguely suspected for quite some time, 
error_operand_p can be useful also outside the c++ front-end. The below, 
which I bootstrapped c, c++, go, on x86_64-linux (and I'm finishing 
testing) tries to do that, moving the macro one level up and using it in 
all the suitable places I spotted.

What do people think?

Thanks,
Paolo.

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