Deduces function signature in thunk

This has been a dream of mine for years. I wanted to remove the explicit
function signatures from day one, but with c++0x it just wasn't
possible. Today, we realize a newer C++, and a brighter world.

Test: build and boot pie
Change-Id: I183be73ece7b6d39630b25ef8fa1f5d4f5a15a2d