Merge #21447: Always add -daemonwait to known command line arguments

4d008f908e Always add -daemonwait to known command line arguments (Hennadii Stepanov)

Pull request description:

  This is a follow up of #21007.

  When `AC_CHECK_DECLS([fork])` fails:

  - on master (8e6532053f):
  ```
  $ src/bitcoind -daemonwait
  Error: Error parsing command line arguments: Invalid parameter -daemonwait

  ```

  - with this PR:
  ```
  $ src/bitcoind -daemonwait
  Error: -daemon is not supported on this operating system

  ```

ACKs for top commit:
  laanwj:
    Code review ACK 4d008f908e

Tree-SHA512: 7fcb5e9d76958adcf57e04fa74bd2a98d62459d81a3c57a97bd74c346cbf47c53e560a15455fb024e912c3b44e8487a83499e993b282871ba069953e665d88a9

src/init.cpp

@@ -585,6 +585,7 @@ void SetupServerArgs(NodeContext& node)
     argsman.AddArg("-daemonwait", strprintf("Wait for initialization to be finished before exiting. This implies -daemon (default: %d)", DEFAULT_DAEMONWAIT), ArgsManager::ALLOW_BOOL, OptionsCategory::OPTIONS);
 #else
     hidden_args.emplace_back("-daemon");
+    hidden_args.emplace_back("-daemonwait");
 #endif
 
     // Add the hidden options