Fix control flow reaches end of non-void function warning

ConflictSet.cpp

@@ -2494,6 +2494,8 @@ checkMaxBetweenExclusive(Node *n, int begin, int end,
   case Type_Node256:
     return checkMaxBetweenExclusiveImpl<true>(static_cast<Node256 *>(n), begin,
                                               end, readVersion, tls);
+  default:                   // GCOVR_EXCL_LINE
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 }
 __attribute__((target("default")))
@@ -2517,6 +2519,8 @@ bool checkMaxBetweenExclusive(Node *n, int begin, int end,
   case Type_Node256:
     return checkMaxBetweenExclusiveImpl<false>(static_cast<Node256 *>(n), begin,
                                                end, readVersion, tls);
+  default:                   // GCOVR_EXCL_LINE
+    __builtin_unreachable(); // GCOVR_EXCL_LINE
   }
 }