[expr.const] Fix example of integral constant expression conversion to

involve integral constant expressions.

Fixes #1627.

Author: zygoloid

source/expressions.tex

@@ -5259,14 +5259,14 @@
 struct A {
   constexpr A(int i) : val(i) { }
   constexpr operator int() const { return val; }
-  constexpr operator long() const { return 43; }
+  constexpr operator long() const { return 42; }
 private:
   int val;
 };
 template<int> struct X { };
-constexpr A a = 42;
-X<a> x;             // OK: unique conversion to \tcode{int}
-int ary[a];         // error: ambiguous conversion
+constexpr A a = alignof(int);
+alignas(a) int n;              // error: ambiguous conversion
+struct B { int n : a; };       // error: ambiguous conversion
 \end{codeblock}
 \end{example}%
 \indextext{expression|)}