Merge pull request #4590 from yang-g/unreachable

fix one use of unreachable macro
diff --git a/src/core/compression/algorithm.c b/src/core/compression/algorithm.c
index 8e4e5c9..51cd54f 100644
--- a/src/core/compression/algorithm.c
+++ b/src/core/compression/algorithm.c
@@ -139,9 +139,9 @@
     case GRPC_COMPRESS_LEVEL_HIGH:
       return GRPC_COMPRESS_DEFLATE;
     default:
-      break;
+      gpr_log(GPR_ERROR, "Unknown compression level %d.", (int)level);
+      abort();
   }
-  GPR_UNREACHABLE_CODE(return GRPC_COMPRESS_NONE);
 }
 
 void grpc_compression_options_init(grpc_compression_options *opts) {