Improve the QT_NAMESPACE definition in Qt6CoreExtras

The perivous version generated weird condition, and seems changing
the QT_NAMESPACE after qtbase configuration is noop, we may replace
the generated condition with the conditional generation.

Change-Id: Ifa09dba4db00099a07da2cff5505e6fd0b008289
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtModuleHelpers.cmake

@@ -683,8 +683,16 @@ function(qt_internal_add_module target)
         list(APPEND extra_cmake_files "${CMAKE_CURRENT_LIST_DIR}/${INSTALL_CMAKE_NAMESPACE}${target}Macros.cmake")
         list(APPEND extra_cmake_includes "${INSTALL_CMAKE_NAMESPACE}${target}Macros.cmake")
     endif()
+
     if (EXISTS "${CMAKE_CURRENT_LIST_DIR}/${INSTALL_CMAKE_NAMESPACE}${target}ConfigExtras.cmake.in")
         if(target STREQUAL Core)
+            if(NOT "${QT_NAMESPACE}" STREQUAL "")
+                string(JOIN "" qtcore_namespace_definition
+                    "set_property(TARGET \${__qt_core_target} "
+                    "APPEND PROPERTY INTERFACE_COMPILE_DEFINITIONS QT_NAMESPACE=${QT_NAMESPACE})"
+                )
+            endif()
+
             set(extra_cmake_code "")
             # Add some variables for compatibility with Qt5 config files.
             if(QT_FEATURE_reduce_exports)

src/corelib/Qt6CoreConfigExtras.cmake.in

@@ -19,9 +19,7 @@ if (NOT QT_NO_CREATE_TARGETS)
         set(__qt_core_target "${__qt_core_aliased_target}")
     endif()
     unset(__qt_core_aliased_target)
-    if (NOT "@QT_NAMESPACE@" STREQUAL "")
-        set_property(TARGET ${__qt_core_target} APPEND PROPERTY INTERFACE_COMPILE_DEFINITIONS QT_NAMESPACE=@QT_NAMESPACE@)
-    endif()
+    @qtcore_namespace_definition@
     set_property(TARGET ${__qt_core_target} APPEND PROPERTY INTERFACE_COMPILE_DEFINITIONS $<$<NOT:$<CONFIG:Debug>>:QT_NO_DEBUG>)
     set_property(TARGET ${__qt_core_target} PROPERTY INTERFACE_COMPILE_FEATURES cxx_decltype)
 endif()