[stackprotector] Implement the sspstrong rules for stack layout.

This changes the PrologueEpilogInserter and LocalStackSlotAllocation passes to
follow the extended stack layout rules for sspstrong and sspreq.

The sspstrong layout rules are:
 1. Large arrays and structures containing large arrays (>= ssp-buffer-size)
are closest to the stack protector.
 2. Small arrays and structures containing small arrays (< ssp-buffer-size) are
2nd closest to the protector.
 3. Variables that have had their address taken are 3rd closest to the
protector.


Differential Revision: http://llvm-reviews.chandlerc.com/D2546