Leak fix: delete old objects before reallocation in an assignment operator!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7055 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineInstr.h

@@ -190,6 +190,8 @@ public:
   }
   
   const MachineOperand &operator=(const MachineOperand &MO) {
+    if (isExternalSymbol())             // if old operand had a symbol name,
+      delete SymbolName;                // release old memory
     immedVal = MO.immedVal;
     flags    = MO.flags;
     opType   = MO.opType;