Fix Qt6 DMG on Apple (#7240)

- Fix linking issues with Qt Framework files
- Fix qmake detection

CMakeLists.txt

@@ -217,12 +217,7 @@ IF(LMMS_BUILD_LINUX AND WANT_VST)
 ENDIF()
 
 # Resolve qmake to full path for use in packaging scripts
-IF(WANT_QT6)
-	FIND_PROGRAM(QT_QMAKE_EXECUTABLE NAME qmake.exe
-		PATHS "${CMAKE_PREFIX_PATH}/bin" /opt/Qt6/bin) # TODO: add more paths here
-ELSE()
-	GET_TARGET_PROPERTY(QT_QMAKE_EXECUTABLE "${Qt5Core_QMAKE_EXECUTABLE}" IMPORTED_LOCATION)
-ENDIF()
+GET_TARGET_PROPERTY(QT_QMAKE_EXECUTABLE Qt${QT_VERSION_MAJOR}::qmake IMPORTED_LOCATION)
 
 # Find the location of Qt translation files
 execute_process(COMMAND ${QT_QMAKE_EXECUTABLE} -query QT_INSTALL_TRANSLATIONS

cmake/apple/install_apple.sh.in

@@ -16,6 +16,9 @@ echo -e "$MSG_COLOR\n\nCreating App Bundle \"$APP\"...$COLOR_RESET"
 qtpath="$(dirname "@QT_QMAKE_EXECUTABLE@")"
 export PATH="$PATH:$qtpath"
 
+# Qt6: Fix @rpath bug https://github.com/orgs/Homebrew/discussions/2823
+ln -sf "$qtpath/../lib" "@CMAKE_BINARY_DIR@/lib"
+
 # Remove any old .app bundles
 rm -Rf "$APP"