Fix CheckBaselineExpectations returning 2 when it can't read its input
file. Since this was originally just in main, convert it to std::exit.

Change-Id: I70ae6fbc6e5e12b748d2ab1cc83b1deb67a8f861
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1710659
Auto-Submit: Dan Elphick <delphick@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62833}