SIL: add an explicit move assignment operation instantiation

Author: compnerd

include/swift/SIL/SILValue.h

@@ -587,6 +587,7 @@ class Operand {
   Operand &operator=(const Operand &use) = delete;
 
   Operand(Operand &&) = default;
+  Operand &operator=(Operand &&) = default;
 
   /// Return the current value being used by this operand.
   SILValue get() const { return TheValue; }