swift234

IRGen: Clear up dtor special cases in SIL-IRGen.

Change the destroying destructor entry point ABI to take 'this' as the appropriate type instead of as %swift.refcounted. Emit the deallocating destructor in IRGen when we see the ClassDecl, not when we see the SILFunction for the destructor. This frees us from having to worry about whether a SILFunction came from a destructor decl. We won't be able to reconstruct that once SILFunctions are pre-mangled.

While we're here, repaint some bikesheds so it's clearer that SIL and SILGen work with the destroying destructor.

Swift SVN r4908