Improve vasm pretty-printing

Summary: This gives each Vinstr an IRInstruction* instead of a SrcKey for the sake
of keeping track of where each vasm instruction came from. AsmInfo has
also been split out into its own header along with some additional
helper functions. We've also added mappings from IRInstruction to
TcaRange and from Block to TcaRange for cold and frozen code regions.

Also fixed a bug where were uninentionally duplicating a Vout struct,
causing us to miss setting the origin IRInstruction for many of the
Vinstrs while emitting vasm.

Reviewed By: @edwinsmith

Differential Revision: D1525064
Include PDOException in stdlib hhi files.

Summary: Closes https://github.com/facebook/hhvm/pull/3719

Reviewed By: @ptarjan

Differential Revision: D1547324