Suppress warnings about missing placement delete. This should now be std-conformant even if compiled with exceptions on.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51429 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/User.h

@@ -242,7 +242,12 @@ public:
   ~User() {
     Use::zap(OperandList, OperandList + NumOperands);
   }
+  /// operator delete - free memory allocated for User and Use objects
   void operator delete(void *Usr);
+  /// placement delete - required by std, but never called.
+  void operator delete(void*, unsigned) {
+    assert(0 && "Constructor throws?");
+  }
   template <unsigned Idx> Use &Op() {
     return OperandTraits<User>::op_begin(this)[Idx];
   }