[XRay] Implement the `llvm-xray graph` subcommand

Here we define the `graph` subcommand which generates a graph from the function
call information and uses it to present the call information graphically with
additional annotations.

Reviewers: dblaikie, dberris

Differential Revision: https://reviews.llvm.org/D27243

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292156 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed