[clang] [BoundsSafety][Sema] Allow counted_by and counted_by_or_null on pointers where the pointee type is incomplete but potentially completable (PR #106321)

[via cfe-commits]

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@@ -2445,6 +2445,26 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
     return !isFunctionType();
   }
 
+  /// \returns True if the type is incomplete and it is also a type that
+  /// cannot be completed by a later type definition.
+  ///
+  /// E.g. For `void` this is true but for `struct ForwardDecl;` this is false
+  /// because a definition for `ForwardDecl` could be provided later on in the
+  /// translation unit.
+  ///
+  /// Note even for types that this function returns true for it is still
+  /// possible for the declarations that contain this type to later have a
+  /// complete type in a translation unit. E.g.:
+  ///
+  /// \code{.c}
+  /// // This decl has type 'char[]' which is incomplete and cannot be later
+  /// // completed by another by another type declaration.
+  /// extern char foo[];
+  /// // This decl how has complete type 'char[5]'.
----------------
Sirraide wrote:

```suggestion
  /// // This decl now has complete type 'char[5]'.
```
typo

https://github.com/llvm/llvm-project/pull/106321