[llvm] [llvm-profgen] Add --time-profgen (PR #191930)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> > > Shall we name it `--time-trace`? Same as what `opt` uses.
> > 
> > 
> > Let me replace with time-trace but it's arbitrary: e.g. in bolt we use time-rewrite for the full pipeline timing, time-opts for optimizations passes, time-aggr for profile work. So the naming is up to you
> 
> I still prefer `--time-trace` to be consistent with other tools, unless we plan to time different parts of the profgen separately in the future. Otherwise, LGTM.

I've looked at use of time-trace in opt and other tools and it's a bit different: 
- time-trace produces a json/trace (viewable by chrome://tracing), not a plain text report,
- uses a different timer infra (NamedRegionTimer -> TimeTraceScope; TimeProfiler.h instead of Timer.h). 

Just confirming this is what you wanted.

https://github.com/llvm/llvm-project/pull/191930