Summary:
This patch moves out the definition of the XRay log file header from
binary logs into its own header and implementation file.
This is one part of the refactoring being done in D50441.
Reviewers: eizan
Subscribers: mgorny, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D51086
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340389 91177308-0d34-0410-b5e6-96231b3b80d8
