Skip unnecessary commands when cross-building tools

Call qt_internal_return_unless_building_tools() directly after
qt_internal_add_tool() to avoid having to special-case code for when
this function only creates imported targets in cross-builds.

Task-number: QTBUG-85084
Change-Id: I1830d4e2b9006d1f789ec4889a01bbb66f63ff11
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/tools/qtwaylandscanner/CMakeLists.txt

@@ -11,6 +11,7 @@ qt_internal_add_tool(${target_name}
     SOURCES
         qtwaylandscanner.cpp
 )
+qt_internal_return_unless_building_tools()
 
 #### Keys ignored in scope 1:.:.:qtwaylandscanner.pro:<TRUE>:
 # _OPTION = "host_build"