[XRay] Fix TSC and atomic custom/typed event accounting
Summary:
This is a follow-on change to D53858 which turns out to have had a TSC
accounting bug when writing out function exit records in FDR mode.
This change adds a number of tests to ensure that:
- We are handling the delta between the exit TSC and the last TSC we've
seen.
- We are writing the custom event and typed event records as a single
update to the buffer extents.
- We are able to catch boundary conditions when loading FDR logs.
We introduce a TSC matcher to the test helpers, which we use in the
testing/verification of the TSC accounting change.
Reviewers: mboerger
Subscribers: mgorny, hiraditya, jfb, llvm-commits
Differential Revision: https://reviews.llvm.org/D53967
llvm-svn: 345905