I couldn't get it to work. It would be nice, because it would more or
less eliminate the need for asm in setting up BUGs - particularly the
nasty asm setting up the structure.
But it just doesn't work. The label &&l ends up pointing to is not
anywhere near the __builtin_trap instruction; I found it tended to point
to the start of the function prologue.
I reported it as a gcc bug, but they refused to hear of it. Details at