Fix an old-style doxygen comment.
Clean up the formatting and doxygen for the simple inliner a bit. No
functionality changed.
Formatting and comment fixes to the always inliner.

Formatting fixes brought to you by clang-format.
Make the inline cost a proper analysis pass. This remains essentially
a dynamic analysis done on each call to the routine. However, now it can
use the standard pass infrastructure to reference other analyses,
instead of a silly setter method. This will become more interesting as
I teach it about more analysis passes.

This updates the two inliner passes to use the inline cost analysis.
Doing so highlights how utterly redundant these two passes are. Either
we should find a cheaper way to do always inlining, or we should merge
the two and just fiddle with the thresholds to get the desired behavior.
I'm leaning increasingly toward the latter as it would also remove the
Inliner sub-class split.