Fix -Wsfinae-incomplete warnings when building with GCC 16.x

[hebasto]

According to the CMake documentation for AUTOMOC, all moc output files that are not included in a source file are aggregated into the CMake-generated <AUTOGEN_BUILD_DIR>/mocs_compilation.cpp, which is added to the target's sources.

Within that single translation unit, moc-generated code checks the completeness of a signal or slot parameter type while it is still only forward-declared, and the type is completed later, when a subsequently included moc_*.cpp file pulls in the header that defines it. GCC 16.x diagnoses this pattern with the -Wsfinae-incomplete warning, which is enabled by default.

Including the moc output files at the end of the corresponding source files excludes them from mocs_compilation.cpp, so each one is compiled in a translation unit where the relevant types are complete.

FWIW, Qt itself uses the same approach throughout its own codebase. Also see https://www.youtube.com/watch?v=Cx_m-qVnEjo.

---

Steps to reproduce on the master branch @ 18c05d9 on Fedora 44 (GCC 16.1.1):

$ cmake --preset dev-mode
$ cmake --build build_dev_mode -t bitcoind
$ cmake --build build_dev_mode -t bitcoin-qt
[166/172] Building CXX object src/qt/CMakeFiles/bitcoinqt.dir/bitcoinqt_autogen/mocs_compilation.cpp.o
In file included from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_bitcoingui.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:9:
/home/hebasto/dev/bitcoin-gui/src/qt/bitcoingui.h:67:7: warning: defining ‘BitcoinGUI’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   67 | class BitcoinGUI : public QMainWindow
      |       ^~~~~~~~~~
In file included from /usr/include/qt6/QtCore/qobject.h:19,
                 from /usr/include/qt6/QtWidgets/qwidget.h:10,
                 from /usr/include/qt6/QtWidgets/qdialog.h:9,
                 from /usr/include/qt6/QtWidgets/QDialog:1,
                 from /home/hebasto/dev/bitcoin-gui/src/qt/addressbookpage.h:8,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_addressbookpage.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:2:
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
In file included from /home/hebasto/dev/bitcoin-gui/src/qt/paymentserver.h:35,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_paymentserver.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:27:
/home/hebasto/dev/bitcoin-gui/src/qt/sendcoinsrecipient.h:15:7: warning: defining ‘SendCoinsRecipient’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   15 | class SendCoinsRecipient
      |       ^~~~~~~~~~~~~~~~~~
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
In file included from /home/hebasto/dev/bitcoin-gui/src/qt/psbtoperationsdialog.h:13,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_psbtoperationsdialog.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:30:
/home/hebasto/dev/bitcoin-gui/src/qt/walletmodel.h:48:7: warning: defining ‘WalletModel’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   48 | class WalletModel : public QObject
      |       ^~~~~~~~~~~
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
In file included from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_qvalidatedlineedit.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:32:
/home/hebasto/dev/bitcoin-gui/src/qt/qvalidatedlineedit.h:13:7: warning: defining ‘QValidatedLineEdit’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   13 | class QValidatedLineEdit : public QLineEdit
      |       ^~~~~~~~~~~~~~~~~~
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
In file included from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_rpcconsole.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:37:
/home/hebasto/dev/bitcoin-gui/src/qt/rpcconsole.h:43:7: warning: defining ‘RPCConsole’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   43 | class RPCConsole: public QWidget
      |       ^~~~~~~~~~
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
In file included from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/EWIEGA46WW/moc_sendcoinsentry.cpp:9,
                 from /home/hebasto/dev/bitcoin-gui/build_dev_mode/src/qt/bitcoinqt_autogen/mocs_compilation.cpp:39:
/home/hebasto/dev/bitcoin-gui/src/qt/sendcoinsentry.h:26:7: warning: defining ‘SendCoinsEntry’, which previously failed to be complete in a SFINAE context [-Wsfinae-incomplete=]
   26 | class SendCoinsEntry : public QWidget
      |       ^~~~~~~~~~~~~~
/usr/include/qt6/QtCore/qmetatype.h:344:64: note: here.  Use ‘-Wsfinae-incomplete=2’ for a diagnostic at that point
  344 |         static auto check(U *) -> std::integral_constant<bool, sizeof(U) != 0>;
      |                                                                ^~~~~~~~~
[172/172] Linking CXX executable bin/bitcoin-qt

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🚧 At least one of the CI tasks failed.
_{Task lint: https://github.com/bitcoin-core/gui/actions/runs/29695312658/job/88214942136
LLM reason (✨ experimental): CI failed because the lint-includes check detected C++ files including .cpp sources (triggering a lint “all_python_linters” failure).}

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[hebasto]

Friendly ping @maflcko @l0rinc