Separate check failure message parts more clearly.

This CL encompasses two changes:

1. Always end check failure messages with a period.
2. In fuzzing mode, replace the period with a semicolon.

For example:

  CHECK(false);

Yields:

  Check failed: false.

Or, with additional data streamed in:

  CHECK(false) << "foo";

The output is:

  Check failed: false. foo

In fuzzing mode, however, in a bid to help machines understand where
to draw the line between the compile-time static part ("false") and
the runtime-variable part ("foo"), we use a semicolon instead. It
seems quite difficult to manage to embed a semilicon in the
compile-time static part. Thus the examples above become:

  Check failed: false;
  Check failed: false; foo

Change-Id: Ia09851382f0d3207d0720d204cef26e223ade024
Bug: 443588668
Cq-Include-Trybots: luci.chromium.try:chromeos-x64-libfuzzer-asan-rel-tests,linux-x64-libfuzzer-asan-dbg-tests,linux-x64-libfuzzer-asan-rel-tests,linux-x64-libfuzzer-msan-rel-tests,linux-x64-libfuzzer-ubsan-rel-tests,linux-x86-libfuzzer-asan-rel-tests,mac-arm64-libfuzzer-asan-rel-tests,win-x64-libfuzzer-asan-rel-tests,linux-x64-centipede-asan-rel-tests
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6917708
Reviewed-by: Antonio Alphonse <alphonsea@google.com>
Commit-Queue: Antonio Alphonse <alphonsea@google.com>
Auto-Submit: Titouan Rigoudy <titouan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1558298}