CMake: Make qtwaylandscanner depend on QtCore only

It doesn't use any Gui classes at the moment.
It also ensures a target dependency cycle is not created on the
default_qpa_plugins custom target when the QT_QPA_DEFAULT_PLATFORM
cache var is set to 'wayland'.

Change-Id: I8958e5b993ad40294abf49f633d1ef31b6c633bb
Reviewed-by: David Edmundson <davidedmundson@kde.org>

src/tools/qtwaylandscanner/.prev_CMakeLists.txt

@@ -8,8 +8,6 @@ qt_get_tool_target_name(target_name qtwaylandscanner)
 qt_internal_add_tool(${target_name}
     SOURCES
         qtwaylandscanner.cpp
-    PUBLIC_LIBRARIES
-        Qt::Gui
 )
 
 #### Keys ignored in scope 1:.:.:qtwaylandscanner.pro:<TRUE>:

src/tools/qtwaylandscanner/CMakeLists.txt

@@ -9,8 +9,6 @@ qt_internal_add_tool(${target_name}
     TOOLS_TARGET WaylandScanner # special case
     SOURCES
         qtwaylandscanner.cpp
-    PUBLIC_LIBRARIES
-        Qt::Gui
 )
 
 #### Keys ignored in scope 1:.:.:qtwaylandscanner.pro:<TRUE>:

src/tools/qtwaylandscanner/qtwaylandscanner.pro

@@ -1,6 +1,7 @@
 option(host_build)
 
 SOURCES += qtwaylandscanner.cpp
+QT = core
 
 load(qt_tool)