Roll-forward: Honor ABSL_MIN_LOG_LEVEL in CHECK_XX, CHECK_STRXX, CHECK_OK, and the QCHECK flavors of these.

In particular, if ABSL_MIN_LOG_LEVEL exceeds kFatal, these should, upon failure, terminate the program without logging anything.  The lack of logging should be visible to the optimizer so that it can strip string literals and stringified variable names from the object file.

Making some edge cases work under Clang required rewriting NormalizeLogSeverity to help make constraints on its return value more obvious to the optimizer.

PiperOrigin-RevId: 588181755
Change-Id: I95db3bae39f8dadb52a307ca3b80775db23de766