Add clang::lifetimebound annotation to ArrayRef constructors. (llvm#113547)

This enables clang to detect more dangling issues.

```
ArrayRef<int> func() {
   constexpr int array[] = {...}; // oops, missing the static
   return array; // return a dangling reference, bomb.
}
```

See llvm#113533.

Author: hokein

llvm/include/llvm/ADT/ArrayRef.h

@@ -70,15 +70,16 @@ namespace llvm {
     /*implicit*/ ArrayRef(std::nullopt_t) {}
 
     /// Construct an ArrayRef from a single element.
-    /*implicit*/ ArrayRef(const T &OneElt)
-      : Data(&OneElt), Length(1) {}
+    /*implicit*/ ArrayRef(const T &OneElt LLVM_LIFETIME_BOUND)
+        : Data(&OneElt), Length(1) {}
 
     /// Construct an ArrayRef from a pointer and length.
-    constexpr /*implicit*/ ArrayRef(const T *data, size_t length)
+    constexpr /*implicit*/ ArrayRef(const T *data LLVM_LIFETIME_BOUND,
+                                    size_t length)
         : Data(data), Length(length) {}
 
     /// Construct an ArrayRef from a range.
-    constexpr ArrayRef(const T *begin, const T *end)
+    constexpr ArrayRef(const T *begin LLVM_LIFETIME_BOUND, const T *end)
         : Data(begin), Length(end - begin) {
       assert(begin <= end);
     }
@@ -103,7 +104,8 @@ namespace llvm {
 
     /// Construct an ArrayRef from a C array.
     template <size_t N>
-    /*implicit*/ constexpr ArrayRef(const T (&Arr)[N]) : Data(Arr), Length(N) {}
+    /*implicit*/ constexpr ArrayRef(const T (&Arr LLVM_LIFETIME_BOUND)[N])
+        : Data(Arr), Length(N) {}
 
     /// Construct an ArrayRef from a std::initializer_list.
 #if LLVM_GNUC_PREREQ(9, 0, 0)
@@ -113,7 +115,8 @@ namespace llvm {
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Winit-list-lifetime"
 #endif
-    constexpr /*implicit*/ ArrayRef(const std::initializer_list<T> &Vec)
+    constexpr /*implicit*/ ArrayRef(
+        std::initializer_list<T> Vec LLVM_LIFETIME_BOUND)
         : Data(Vec.begin() == Vec.end() ? (T *)nullptr : Vec.begin()),
           Length(Vec.size()) {}
 #if LLVM_GNUC_PREREQ(9, 0, 0)

llvm/include/llvm/Support/Compiler.h

@@ -307,6 +307,12 @@
 #define LLVM_GSL_POINTER
 #endif
 
+#if LLVM_HAS_CPP_ATTRIBUTE(clang::lifetimebound)
+#define LLVM_LIFETIME_BOUND [[clang::lifetimebound]]
+#else
+#define LLVM_LIFETIME_BOUND
+#endif
+
 #if LLVM_HAS_CPP_ATTRIBUTE(nodiscard) >= 201907L
 #define LLVM_CTOR_NODISCARD [[nodiscard]]
 #else