Improve logging when signaling a semaphore fails

That change is attempting to surface the root cause of a recent flake,
see the related bug.

Bug: v8:8228
Change-Id: Iebed5b8f46db3fd47154031856dc7ea173cf3d7f
Reviewed-on: https://chromium-review.googlesource.com/1245771Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56244}

src/base/platform/semaphore.cc

@@ -91,7 +91,9 @@ void Semaphore::Signal() {
   // This check may fail with <libc-2.21, which we use on the try bots, if the
   // semaphore is destroyed while sem_post is still executed. A work around is
   // to extend the lifetime of the semaphore.
-  CHECK_EQ(0, result);
+  if (result != 0) {
+    FATAL("Error when signaling semaphore, errno: %d", errno);
+  }
 }