[CallGraph] Given -print-callgraph a stable printing order.
Since FunctionMap has llvm::Function pointers as keys, the order in
which the traversal happens can differ from run to run, causing spurious
FileCheck failures. Have CallGraph::print sort the CallGraphNodes by
name before printing them.
Reviewers: bogner, chandlerc
Differential Revision: http://reviews.llvm.org/D10575