CMakeLists: Allow for internal plugin registration

add_qtc_plugin now takes a flag "INTERNAL_ONLY". These internal plugins
will not show up in the project configuration nor in the feature summary.

This flag is used by the tests that build plugins.

Change-Id: I1912dd62221b2624ed7326df381fbbceccefbdac
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

tests/auto/extensionsystem/pluginmanager/circularplugins/plugin1/CMakeLists.txt

@@ -4,4 +4,5 @@ add_qtc_plugin(plugin1
     plugin1.cpp plugin1.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
- )
+  INTERNAL_ONLY
+)

tests/auto/extensionsystem/pluginmanager/circularplugins/plugin2/CMakeLists.txt

@@ -4,4 +4,5 @@ add_qtc_plugin(plugin2
     plugin2.cpp plugin2.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
- )
+  INTERNAL_ONLY
+)

tests/auto/extensionsystem/pluginmanager/circularplugins/plugin3/CMakeLists.txt

@@ -4,4 +4,5 @@ add_qtc_plugin(plugin3
     plugin3.cpp plugin3.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
- )
+  INTERNAL_ONLY
+)

tests/auto/extensionsystem/pluginmanager/correctplugins1/plugin1/CMakeLists.txt

@@ -5,4 +5,5 @@ add_qtc_plugin(correct_plugin1
     plugin1.cpp plugin1.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
+  INTERNAL_ONLY
 )

tests/auto/extensionsystem/pluginmanager/correctplugins1/plugin2/CMakeLists.txt

@@ -5,4 +5,5 @@ add_qtc_plugin(correct_plugin2
     plugin2.cpp plugin2.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
+  INTERNAL_ONLY
 )

tests/auto/extensionsystem/pluginmanager/correctplugins1/plugin3/CMakeLists.txt

@@ -5,4 +5,5 @@ add_qtc_plugin(correct_plugin3
     plugin3.cpp plugin3.h
   PLUGIN_PATH "${TEST_PLUGIN_PATH}"
   SKIP_INSTALL
+  INTERNAL_ONLY
 )