DynamicYield: no more prepareXXX functions

Summary: yup

Reviewed By: @jano

Differential Revision: D1580123
Add --list-tests option

Summary: This will be used by the new test-runner-runner @ fb.

Reviewed By: @JoelMarcey

Differential Revision: D1579422
Fixup origins during vasm immediate folding

Summary: I noticed we were missing seemingly random vasm instructions in
our assembly dumps. I tracked it down to the immediate folding, which
would replace the old Vinstr containing a valid IRInstruction origin
with a new Vinstr with no origin set.

Reviewed By: @edwinsmith

Differential Revision: D1579895
Add new quick hull benchmark

Summary: Added a new benchmark named QuickHull that computes the convex hull of
1000 points using the quick hull algorithm (see:
http://stackoverflow.com/a/18418182). The benchmark leans heavily on
struct-like arrays for representing points and line equations. It also
makes frequent use of some array_* library intrinsics (e.g. array_reduce).

Reviewed By: @jdelong

Differential Revision: D1573015
Fix LowStringPtr pretty printer

Summary: My LowStringPtrs have always printed out as "LowStringPtr '(type str)'"
and I just figured out why.

Reviewed By: @mxw

Differential Revision: D1578616