CMake: Guard examples that use Svg in a qt build without Svg

Otherwise one gets errors like the following in standalone examples
build:
  CMake Error at tools/svgtoqml/Qt6SvgToQmlMacros.cmake:65
    (add_custom_command):
  Error evaluating generator expression:
    $
    No target "Qt6::svgtoqml"

Because the examples now use the new qt_target_qml_from_svg()
function, which will try to reference a non-existent svgtoqml tool
target.

Change-Id: I16b10c4fa31bd73d0d95bbad371cde54f17c236a
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

examples/quick/CMakeLists.txt

@@ -40,7 +40,9 @@ if(TARGET Qt6::QuickWidgets AND TARGET Qt6::Widgets AND (QT_FEATURE_opengl OR QT
 endif()
 add_subdirectory(quickshapes)
 qt_internal_add_example(advancedtext)
+if(TARGET Qt6::Svg)
     qt_internal_add_example(vectorimage)
+endif()
 
 # qt_examples_build_end() misses at least some of these due to some
 # source subdirectories being added multiple times. See QTBUG-96159.

examples/quick/quickshapes/CMakeLists.txt

@@ -1,12 +1,16 @@
 # Copyright (C) 2024 The Qt Company Ltd.
 # SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
-qt_internal_add_example(shapes)
-qt_internal_add_example(weatherforecast)
-
 # qt_examples_build_end() misses at least some of these due to some
 # source subdirectories being added multiple times. See QTBUG-96159.
-set(reused_dir_targets shapes_shared weatherforecast_shared)
+set(reused_dir_targets shapes_shared)
+
+qt_internal_add_example(shapes)
+
+if(TARGET Qt6::Svg)
+    list(APPEND reused_dir_targets weatherforecast_shared)
+    qt_internal_add_example(weatherforecast)
+endif()
 
 foreach(target IN LISTS reused_dir_targets)
     if(TARGET ${target})