Update CMakeLists.txt to support both Qt5 and Qt6. Add option ENABLE_QT6

plugins/samplesource/fcdproplus/CMakeLists.txt

@@ -35,7 +35,7 @@ if(NOT SERVER_MODE)
     )
 
     set(TARGET_NAME inputfcdproplus)
-    set(TARGET_LIB "Qt5::Widgets")
+    set(TARGET_LIB "Qt::Widgets")
     set(TARGET_LIB_GUI "sdrgui")
     set(INSTALL_FOLDER ${INSTALL_PLUGINS_DIR})
 else()
@@ -51,7 +51,7 @@ add_library(${TARGET_NAME} SHARED
 
 target_link_libraries(${TARGET_NAME}
     ${HIDAPI_LIBRARIES}
-    Qt5::Core
+    Qt::Core
     ${TARGET_LIB}
 	sdrbase
 	${TARGET_LIB_GUI}