[Test][Time profiler] Fix test time checking

[anton-afanasyev]

Summary

This test sometimes triggers failures during build testing. For instance, see:
https://lab.llvm.org/buildbot/#/builders/52/builds/10161, details: https://lab.llvm.org/buildbot/#/builders/52/builds/10161/steps/5/logs/FAIL__Clang__check-time-trace-sections_cpp .
AFAICT the time between driver calling and checking its time tracker output
is not guaranteed to be stable and small:

> head -2 check-time-trace-sections.cpp
// RUN: %clangxx -S -ftime-trace -ftime-trace-granularity=0 -o %T/check-time-trace-sections %s
// RUN: cat %T/check-time-trace-sections.json | %python %S/check-time-trace-sections.py
> clang -S -ftime-trace -ftime-trace-granularity=0 -o /tmp/check check-time-trace-sections.cpp
> cat /tmp/check.json | python check-time-trace-sections.py
> sleep 10
> cat /tmp/check.json | python check-time-trace-sections.py
'beginningOfTime' should represent the absolute time when the process has started
>

The attribute beginningOfTime was introduced here: https://reviews.llvm.org/D78030
One can change "10 sec" value to something longer, but I believe
it's enough just to check that beginningOfTime exists and is
not later than current time.

[lebedev.ri]

Everything timing-based is pretty much guaranteed to be flaky.

clang/test/Driver/check-time-trace-sections.py

 events = log_contents["traceEvents"]
 codegens = [event for event in events if event["name"] == "CodeGen Function"]
 frontends = [event for event in events if event["name"] == "Frontend"]
 backends = [event for event in events if event["name"] == "Backend"]
 
 beginning_of_time = log_contents["beginningOfTime"] / 1000000
 seconds_since_epoch = time.time()
 
-# Make sure that the 'beginningOfTime' is not earlier than 10 seconds ago
-# and not later than now.
-if beginning_of_time > seconds_since_epoch or \
-        seconds_since_epoch - beginning_of_time > 10:
+# Make sure that the 'beginningOfTime' is not later than now.
+if beginning_of_time > seconds_since_epoch:
     sys.exit("'beginningOfTime' should represent the absolute time when the "
              "process has started")
 
 if not all([any([is_inside(codegen, frontend) for frontend in frontends])
                         for codegen in codegens]):
     sys.exit("Not all CodeGen sections are inside any Frontend section!")
 
 if not all([all([is_before(frontend, backend) for frontend in frontends])
                         for backend in backends]):
     sys.exit("Not all Frontend section are before all Backend sections!")