Add test

Author: DKLoehr

clang/test/SemaCXX/unique_object_duplication.h

@@ -99,6 +99,10 @@ inline void has_thread_local() {
   thread_local int disallowedThreadLocal = 0; // hidden-warning {{'disallowedThreadLocal' may be duplicated when built into a shared library: it is mutable, has hidden visibility, and external linkage}}
 }
 
+
+// Functions themselves are always immutable, so referencing them is okay
+auto& allowedFunctionReference = has_static_locals_external;
+
 } // namespace StaticLocalTest
 
 /******************************************************************************
@@ -154,6 +158,7 @@ namespace GlobalTest {
   };
 
   inline float Test::disallowedStaticMember2 = 2.3; // hidden-warning {{'disallowedStaticMember2' may be duplicated when built into a shared library: it is mutable, has hidden visibility, and external linkage}}
+
 } // namespace GlobalTest
 
 /******************************************************************************