Remove the unnecessary virtual dtor from the DIEUnit hierarchy (in favor of protected dtor in the base, final derived classes with public non-virtual dtors)

These objects are never polymorphically owned/destroyed, so the virtual
dtor was unnecessary.

llvm-svn: 301068
diff --git a/llvm/unittests/DebugInfo/DWARF/DwarfGenerator.h b/llvm/unittests/DebugInfo/DWARF/DwarfGenerator.h
index 966725b..76665e5 100644
--- a/llvm/unittests/DebugInfo/DWARF/DwarfGenerator.h
+++ b/llvm/unittests/DebugInfo/DWARF/DwarfGenerator.h
@@ -138,7 +138,7 @@
 /// contained inside this class.
 class CompileUnit {
   Generator &DG;
-  DIEUnit DU;
+  BasicDIEUnit DU;
 
 public:
   CompileUnit(Generator &D, uint16_t V, uint8_t A)