DataFlowSanitizer; Clang changes.

DataFlowSanitizer is a generalised dynamic data flow analysis.

Unlike other Sanitizer tools, this tool is not designed to detect a
specific class of bugs on its own.  Instead, it provides a generic
dynamic data flow analysis framework to be used by clients to help
detect application-specific issues within their own code.

Differential Revision: http://llvm-reviews.chandlerc.com/D966

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187925 91177308-0d34-0410-b5e6-96231b3b80d8