[esan|wset] Add working set tool driver flags

Summary:
Adds a new -fsanitize=efficiency-working-set flag to enable esan's working
set tool.  Adds appropriate tests for the new flag.

Reviewers: aizatsky

Subscribers: vitalybuka, zhaoqin, kcc, eugenis, llvm-commits

Differential Revision: http://reviews.llvm.org/D20484

llvm-svn: 270641