Introduce RTC_CHECK_NOTREACHED(), an always-checking RTC_NOTREACHED()

And use it in a few places that were using RTC_CHECK(false) or FATAL()
to do the exact same job. There should be no change in behavior.

Bug: none
Change-Id: I36d5e6bcf35fd41534e08a8c879fa0811b4f1967
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/191963
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32567}
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index 165968c..3760a01 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -2408,7 +2408,7 @@
                                   GetIceCandidatePairCounter(local, remote),
                                   kIceCandidatePairMax);
       } else {
-        RTC_CHECK(0);
+        RTC_CHECK_NOTREACHED();
       }
 
       // Increment the counter for IP type.