Added short CMake option USE_QT6 to enable Qt6 support

CMakeLists.txt

@@ -68,6 +68,7 @@ option( USE_ASPELL "Build psi with aspell spellcheck" OFF )
 option( USE_CCACHE "Use ccache utility if found" ON )
 option( USE_CRASH "Enable builtin sigsegv handling" OFF )
 option( USE_KEYCHAIN "Enable QtKeychain support" ON )
+option( USE_QT6 "Enable Qt6 support" OFF )
 option( ONLY_BINARY "Build and install only binary file" OFF )
 option( ONLY_PLUGINS "Build psi plugins only" OFF )
 option( INSTALL_EXTRA_FILES "Install sounds, iconsets, certs, client_icons.txt, themes" ON )
@@ -136,6 +137,10 @@ else()
     message(STATUS "Chatlog type - Basic")
 endif()
 
+if(USE_QT6)
+    set(QT_DEFAULT_MAJOR_VERSION 6)
+endif()
+
 message(STATUS "System name - ${CMAKE_SYSTEM_NAME}")
 
 if("${CMAKE_BUILD_TYPE}" STREQUAL "Debug" OR ("${CMAKE_BUILD_TYPE}" STREQUAL "RelWithDebInfo"))