Use Boolean operators compute xor, or, and over bool

Using bitwise xor (^) is an operation over integers, and triggers a warning by
Visual Studio. The same is true for |, &; the latter were only sometimes used
for this purpose, which also makes this a consistency-fix.

Author: tautschnig

src/util/mp_arith.cpp

@@ -269,7 +269,7 @@ mp_integer bitwise_xor(const mp_integer &a, const mp_integer &b)
   if(a.is_ulong() && b.is_ulong())
     return a.to_ulong() ^ b.to_ulong();
 
-  return bitwise(a, b, [](bool a, bool b) { return a ^ b; });
+  return bitwise(a, b, [](bool a, bool b) { return a != b; });
 }
 
 /// arithmetic left shift bitwise operations only make sense on native objects,

src/util/simplify_expr_int.cpp

@@ -734,11 +734,11 @@ bool simplify_exprt::simplify_bitwise(exprt &expr)
     std::function<bool(bool, bool)> f;
 
     if(expr.id()==ID_bitand)
-      f = [](bool a, bool b) { return a & b; };
+      f = [](bool a, bool b) { return a && b; };
     else if(expr.id()==ID_bitor)
-      f = [](bool a, bool b) { return a | b; };
+      f = [](bool a, bool b) { return a || b; };
     else if(expr.id()==ID_bitxor)
-      f = [](bool a, bool b) { return a ^ b; };
+      f = [](bool a, bool b) { return a != b; };
     else
       UNREACHABLE;