[RFC] Don't block on finishing demangling msymbols

Instead, do it all on a background thread and only block when we actually
need the result.

Note, this is a speedup but not quite as much as I was expecting; still
looking into what causes the waits. However, let me know if you have thoughts
on the concept!

Change-Id: I9d871917459ece0b41d31670b3c56600757aea66
2 files changed