opt_inline: code cleanup, use C99

Note that this also fixed the calculation of the "recursive" property
changing the inlining behaviour for some programs.
do not give malus for recursive calls
opt_inline: improve reporting, optimize

- calculate things once per graph rather than once per call where
  possible.
- Always print out reason in debug info if a call/graph can't be inlined.
tweak inline heuristic a bit