Some cleanups for compilation with GCC 4.0.0 to remove warnings:
* Use C++ style casts, not C style casts
* Abstract base classes should have virtual destructor.

llvm-svn: 22057
diff --git a/llvm/lib/VMCore/AsmWriter.cpp b/llvm/lib/VMCore/AsmWriter.cpp
index 889ae40..9ae3b9a 100644
--- a/llvm/lib/VMCore/AsmWriter.cpp
+++ b/llvm/lib/VMCore/AsmWriter.cpp
@@ -34,6 +34,9 @@
 
 namespace llvm {
 
+// Make virtual table appear in this compilation unit.
+AssemblyAnnotationWriter::~AssemblyAnnotationWriter() {}
+
 /// This class provides computation of slot numbers for LLVM Assembly writing.
 /// @brief LLVM Assembly Writing Slot Computation.
 class SlotMachine {