Build fail with M_CORE_GB=OFF

[Ski-lleR]

Hi,

Since i don't use GB/GBC core, i tried to disable them with the param M_CORE_GB=OFF, but if i do that build fail :

/home/unknown/src/mgba/src/platform/qt/MultiplayerController.cpp:19:1: error: no declaration matches ‘QGBA::MultiplayerController::Player::Player(QGBA::CoreController*, GBSIOLockstepNode*)’
   19 | MultiplayerController::Player::Player(CoreController* coreController, GBSIOLockstepNode* node)
      | ^~~~~~~~~~~~~~~~~~~~~
In file included from /home/unknown/src/mgba/src/platform/qt/MultiplayerController.cpp:6:
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.h:47:9: note: candidates are: ‘constexpr QGBA::MultiplayerController::Player::Player(QGBA::MultiplayerController::Player&&)’
   47 |  struct Player {
      |         ^~~~~~
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.h:47:9: note:                 ‘constexpr QGBA::MultiplayerController::Player::Player(const QGBA::MultiplayerController::Player&)’
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.h:52:3: note:                 ‘QGBA::MultiplayerController::Player::Player(QGBA::CoreController*, GBASIOLockstepNode*)’
   52 |   Player(CoreController* controller, GBASIOLockstepNode* node);
      |   ^~~~~~
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.h:47:9: note: ‘struct QGBA::MultiplayerController::Player’ defined here
   47 |  struct Player {
      |         ^~~~~~
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.cpp:19:1: error: ‘struct QGBA::MultiplayerController::Player’ is private within this context
   19 | MultiplayerController::Player::Player(CoreController* coreController, GBSIOLockstepNode* node)
      | ^~~~~~~~~~~~~~~~~~~~~
In file included from /home/unknown/src/mgba/src/platform/qt/MultiplayerController.cpp:6:
/home/unknown/src/mgba/src/platform/qt/MultiplayerController.h:47:9: note: declared private here
   47 |  struct Player {
      |         ^~~~~~
make[2]: *** [qt/CMakeFiles/mgba-qt.dir/build.make:753: qt/CMakeFiles/mgba-qt.dir/MultiplayerController.cpp.o] Error 1
make[2]: *** Attente des tâches non terminées....
make[1]: *** [CMakeFiles/Makefile2:435: qt/CMakeFiles/mgba-qt.dir/all] Error 2
make: *** [Makefile:152: all] Error 2