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/modules/audio_processing/audio_processing_impl.cc b/modules/audio_processing/audio_processing_impl.cc
index 9cf1e1d..56d7073 100644
--- a/modules/audio_processing/audio_processing_impl.cc
+++ b/modules/audio_processing/audio_processing_impl.cc
@@ -114,7 +114,7 @@
     case Agc1Config::kFixedDigital:
       return GainControl::kFixedDigital;
   }
-  RTC_CHECK(false);
+  RTC_CHECK_NOTREACHED();
 }
 
 // Maximum lengths that frame of samples being passed from the render side to
@@ -1830,7 +1830,7 @@
             case NoiseSuppresionConfig::kVeryHigh:
               return NsConfig::SuppressionLevel::k21dB;
           }
-          RTC_CHECK(false);
+          RTC_CHECK_NOTREACHED();
         };
 
     NsConfig cfg;