* spot/tl/formula.hh: Move all throw statements behind
some [[noreturn]] report...() methods...
* spot/tl/formula.cc: ... defined here.  This makes the methods
shorter and helps their inlining.  Incidentally, this also removes the
uninitialized read that weirdly occurs when _GLIBCXX_DEBUG is on, as
observed with #184, but I do not know why.