[llvm] [ADT] Introduce Casting function objects (PR #165803)

[Jakub Kuderski via llvm-commits]

================
@@ -561,6 +562,53 @@ TEST(CastingTest, assertion_check_unique_ptr) {
       << "Invalid cast of const ref did not cause an abort()";
 }
 
+TEST(Casting, StaticCastPredicate) {
+  std::vector<uint32_t> Values{1, 2};
+
+  EXPECT_TRUE(
+      all_of(map_range(Values, StaticCastTo<uint64_t>),
+             [](const auto &V) { return sizeof(V) == sizeof(uint64_t); }));
+}
+
+TEST(Casting, LLVMRTTIPredicates) {
+  struct Base {
+    enum Kind { BK_Base, BK_Derived };
+    const Kind K;
+    Base(Kind K = BK_Base) : K(K) {}
+    Kind getKind() const { return K; }
+    virtual ~Base() = default;
+  };
+
+  struct Derived : public Base {
----------------
kuhar wrote:

```suggestion
  struct Derived :  Base {
```

https://github.com/llvm/llvm-project/pull/165803