Fix a memory correctness error noticed by valgrind (harmless in practice).

Thanks to Duncan Sands for noticing it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46007 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/StringPool.h

@@ -110,7 +110,7 @@ namespace llvm {
         return;
       if (--S->getValue().Refcount == 0) {
         S->getValue().Pool->InternTable.remove(S);
-        delete S;
+        S->Destroy();
       }
       S = 0;
     }