make sure to always inline the callback inside the specialized gc.trace...

make sure to always inline the callback inside the specialized gc.trace functions. This is essential for minor collections, else we do an unnecessary call to _trace_drag_out which costs 5-10% on gcbench

--HG--
branch : gc-custom-trace-memo
2 jobs for branch/gc-custom-trace-memo in 7 minutes and 19 seconds (queued for 3 seconds)