Fix BitVector move ctor/assignment.

[eugenis]

Summary

Current implementation leaves the object in an invalid state.

[dblaikie]

Test coverage?

[eugenis]

In D21423#459571, @dblaikie wrote:

Test coverage?

Of course. Thanks for reminding!

[dblaikie]

Great - thanks!

[eugenis]

r272965

include/llvm/ADT/BitVector.h

BitVector(const BitVector &RHS) : Size(RHS.size()) {
     Capacity = NumBitWords(RHS.size());
     Bits = (BitWord *)std::malloc(Capacity * sizeof(BitWord));
     std::memcpy(Bits, RHS.Bits, Capacity * sizeof(BitWord));
   }
 
   BitVector(BitVector &&RHS)
     : Bits(RHS.Bits), Size(RHS.Size), Capacity(RHS.Capacity) {
     RHS.Bits = nullptr;
+    RHS.Size = RHS.Capacity = 0;
   }
 
   ~BitVector() {
     std::free(Bits);
   }
 
   /// empty - Tests whether there are no bits in this bitvector.
   bool empty() const { return Size == 0; }
const BitVector &operator=(BitVector &&RHS) {
     if (this == &RHS) return *this;
 
     std::free(Bits);
     Bits = RHS.Bits;
     Size = RHS.Size;
     Capacity = RHS.Capacity;
 
     RHS.Bits = nullptr;
+    RHS.Size = RHS.Capacity = 0;
 
     return *this;
   }
 
   void swap(BitVector &RHS) {
     std::swap(Bits, RHS.Bits);
     std::swap(Size, RHS.Size);
     std::swap(Capacity, RHS.Capacity);