Remove the explicit SDNodeIterator::operator= in favor of the implicit default

There doesn't seem to be any need to assert that iterator assignment is
between iterators over the same node - if you want to reuse an iterator
variable to iterate another node, that's perfectly acceptable. Just
don't mix comparisons between iterators into disjoint sequences, as
usual.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231135 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

@@ -548,6 +548,7 @@ public:
   }
   PhiState(Value *b) : status(Base), base(b) {}
   PhiState() : status(Unknown), base(nullptr) {}
+  PhiState &operator=(const PhiState &) = default;
   PhiState(const PhiState &other) : status(other.status), base(other.base) {
     assert(status != Base || base);
   }