[clang] [clang-tools-extra] [libcxx] [clang] Enable sized deallocation by default in C++14 onwards (PR #83774)

[Vitaly Buka via cfe-commits]

vitalybuka wrote:

@ldionne looks like a bug in std::string

```
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1123,7 +1123,7 @@ public:
   inline _LIBCPP_CONSTEXPR_SINCE_CXX20 ~basic_string() {
     __annotate_delete();
     if (__is_long())
-      __alloc_traits::deallocate(__alloc(), __get_long_pointer(), __get_long_cap());
+      __alloc_traits::deallocate(__alloc(), __get_long_pointer(), __get_long_cap() + 1);
   }
 
```

https://github.com/llvm/llvm-project/pull/83774