Auto merge of #68720 - wesleywiser:llvm_time_trace, r=davidtwco

Auto merge of #68720 - wesleywiser:llvm_time_trace, r=davidtwco

Add support for enabling the LLVM time-trace feature

I found this helpful while investigating an LLVM performance issue.
Passing `-Z llvm-time-trace` causes a `llvm_timings.json` file to be
created. This file can be inspected in with the Chrome Profiler
tools or with any other compatible tool like SpeedScope.

More information on the LLVM feature:

- https://aras-p.info/blog/2019/01/16/time-trace-timeline-flame-chart-profiler-for-Clang/

- https://reviews.llvm.org/rL357340