Don't call qt_add_qml_module with inexistent TARGET

If the passed TARGET does not exist (because it had been disabled in the
CMake configuration), qt_add_qml_module will create it for the user.
That created target is by itself incomplete and breaks the build.

So, don't call qt_add_qml_module with inexistent TARGET.

Fixes: QTCREATORBUG-25960
Change-Id: I646eb2176befb0fd5fe06e184ebd0cee32e18ab2
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/libs/tracing/CMakeLists.txt

@@ -47,6 +47,10 @@ if(${Qt5_VERSION} VERSION_LESS "6.2.0")
       qml/tracing.qrc
   )
 else() # < Qt 6.2
+  if (NOT TARGET Tracing)
+    return()
+  endif()
+
   set(TRACING_QML_FILES
     qml/ButtonsBar.qml
     qml/CategoryLabel.qml

src/plugins/perfprofiler/CMakeLists.txt

@@ -52,6 +52,10 @@ if(${Qt5_VERSION} VERSION_LESS "6.2.0")
       perfprofiler.qrc
   )
 else() # < Qt 6.2
+  if (NOT TARGET PerfProfiler)
+    return()
+  endif()
+
   qt_add_resources(PerfProfiler perfprofiler
     PREFIX "/perfprofiler"
     tracepoints.sh

src/plugins/qmlprofiler/CMakeLists.txt

@@ -83,6 +83,10 @@ if(${Qt5_VERSION} VERSION_LESS "6.2.0")
       qml/qmlprofiler.qrc
   )
 else() # < Qt 6.2
+  if (NOT TARGET QmlProfiler)
+    return()
+  endif()
+
   set(QMLPROFILER_QML_FILES
     qml/QmlProfilerFlameGraphView.qml
   )