Implement shortcuts for slow calls (#6084)
Fix up shortcut for slow calls
Comments on slow-call-shortcutting
-ddump-cmm: don't dump the proc point stage if we didn't do anything
Refactor handleRunStatus some more, add comments and tidy up formatting

I liked the idea of combining traceRunStatus and handleRunStatus, but
I think we lost a bit of clarity where traceRunStatus wants to fall
back to handleRunStatus when the breakpoint is enabled.  So I
refactored it a bit more.