clang with c++2a: 'no_destroy' attribute cannot be applied to types

[mumbleskates]

What version of protobuf and what language are you using?
Version: master, first appearing in commit a001250
Language: C++

What operating system (Linux, Windows, ...) and version?
linux (ubuntu 20.10)

What runtime / compiler are you using (e.g., python version or gcc version)
clang 11.0.0-2 in C++2a standard

What did you do?
Steps to reproduce the behavior:

1. CC=clang bazel build --cxxopt='-std=c++2a' //:protobuf
2. observe error: 'no_destroy' attribute cannot be applied to types in basically any generated pb source file (and some non-generated ones)

What did you expect to see
No errors, hopefully. It would be nice. It worked up until now.

What did you see instead?
Compilation failures. One possible result:

src/google/protobuf/duration.pb.cc:32:20: error: 'no_destroy' attribute cannot be applied to types
PROTOBUF_CONSTINIT PROTOBUF_ATTRIBUTE_NO_DESTROY DurationDefaultTypeInternal _Duration_default_instance_;
                   ^
src/google/protobuf/port_def.inc:592:41: note: expanded from macro 'PROTOBUF_ATTRIBUTE_NO_DESTROY'
#define PROTOBUF_ATTRIBUTE_NO_DESTROY [[clang::no_destroy]]
                                        ^

Anything else we should know about your project / environment
Nothing that comes to mind. It's unclear what the problem is here exactly, whether this is misbehavior by LLVM or a mistake in the protobuf library; from what I can tell based on the documentation this does look like the right way to use the annotation.

[mumbleskates]

Oh fantastic, since I went to sleep @Yuhanun opened #8296 with the right answer.