[BitVector] Define BitWord as uintptr_t

Define BitVector::BitWord as uintptr_t instead of unsigned long, as long does not necessarily translates to a pointer size (especially on 64-bit Visual Studio).

Committed on behalf of @ekatz (Ehud Katz)

Differential Revision: https://reviews.llvm.org/D69336

llvm/include/llvm/ADT/BitVector.h

@@ -71,7 +71,7 @@ public:
 };
 
 class BitVector {
-  typedef unsigned long BitWord;
+  typedef uintptr_t BitWord;
 
   enum { BITWORD_SIZE = (unsigned)sizeof(BitWord) * CHAR_BIT };