i#1661 post-syscall pc: provide pc for mcontext in post-syscall event
i#1661 post-syscall pc: provide pc for mcontext in post-syscall event

Although we promise the pc for all syscall events, today we only set it for
pre-syscall.  This CL adds the pc for the post-syscall event.

Fixes #1661

Review-URL: https://codereview.appspot.com/221410043

code4bones/dynamorio,AmesianX/dynamorio,bl4ckic3/dynamorio,sigma-random/dynamorio,code4bones/dynamorio,daksunt/dynamorio,sigma-random/dynamorio,AmesianX/dynamorio,sigma-random/dynamorio,code4bones/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,sigma-random/dynamorio,code4bones/dynamorio,sigma-random/dynamorio,bl4ckic3/dynamorio