Remove a compiler warning.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56478 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CompilerDriver/Plugin.h

@@ -31,6 +31,9 @@ namespace llvmc {
     /// PopulateCompilationGraph - The auto-generated function that
     /// populates the compilation graph with nodes and edges.
     virtual void PopulateCompilationGraph(CompilationGraph&) const = 0;
+
+    /// Needed to avoid a compiler warning.
+    virtual ~BasePlugin() {};
   };
 
   typedef llvm::Registry<BasePlugin> PluginRegistry;