FeatureSummary: Print each feature info only once

If a feature is added multiple times via ADD_FEATURE_INFO it should
appear only once in FEATURE_SUMMARY.
Signed-off-by: Gregor Jasny <gjasny@googlemail.com>

Modules/FeatureSummary.cmake

@@ -379,6 +379,9 @@ function(_FS_GET_FEATURE_SUMMARY _property _var _includeQuiet)
 
   set(_currentFeatureText "")
   get_property(_EnabledFeatures  GLOBAL PROPERTY ${_property})
+  if(_EnabledFeatures)
+    list(REMOVE_DUPLICATES _EnabledFeatures)
+  endif(_EnabledFeatures)
 
   foreach(_currentFeature ${_EnabledFeatures})
 

Tests/RunCMake/FeatureSummary/FeatureSummaryWhatOnce-stdout.txt

+--( )
+ \* Foo , Foo decscription\.
++
+--

Tests/RunCMake/FeatureSummary/FeatureSummaryWhatOnce.cmake

+include(FeatureSummary)
+
+set(WITH_FOO 1)
+
+add_feature_info(Foo WITH_FOO "Foo decscription.")
+add_feature_info(Foo WITH_FOO "Foo decscription.")
+
+feature_summary(WHAT ENABLED_FEATURES)

Tests/RunCMake/FeatureSummary/RunCMakeTest.cmake

@@ -6,3 +6,4 @@ run_cmake(FeatureSummaryWhatSingleUnknown)
 run_cmake(FeatureSummaryWhatList)
 run_cmake(FeatureSummaryWhatListUnknown)
 run_cmake(FeatureSummaryWhatListAll)
+run_cmake(FeatureSummaryWhatOnce)