[Bug c++/123338] New: ICE: Segmentation fault in cp_coroutine_transform with non-class promise_type(eg. int)

[522024330006 at smail dot nju.edu.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123338

            Bug ID: 123338
           Summary: ICE: Segmentation fault in cp_coroutine_transform with
                    non-class promise_type(eg. int)
           Product: gcc
           Version: 15.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 522024330006 at smail dot nju.edu.cn
  Target Milestone: ---

Compiler Explorer: https://godbolt.org/z/Y7KfEzsnM

The code crashed only on gcc trunk.

```c
#include <coroutine>

template<>
struct std::coroutine_traits<int, int> {
    using promise_type = int;
};

int coro(int x) {
    co_return 42;
}
```

Part of the traceback:
```console
 internal compiler error: Segmentation fault
0x290fae8 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
__va_list_tag (*) [1], diagnostics::kind)
        ???:0
0x29048ab internal_error(char const*, ...)
        ???:0
0xbb430d cp_coroutine_transform::build_ramp_function()
        ???:0
0xbb5aba cp_coroutine_transform::apply_transforms()
        ???:0
0xc10461 finish_function(bool)
        ???:0
0xd52ed3 c_parse_file()
        ???:0
0xec4909 c_common_parse_file()
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```