[Bug c/120309] New: internal compiler error: Segmentation fault in groktypename since gcc 15.1

[mario.rodriguezb1 at um dot es via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120309

            Bug ID: 120309
           Summary: internal compiler error: Segmentation fault in
                    groktypename since gcc 15.1
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mario.rodriguezb1 at um dot es
  Target Milestone: ---

ICE only since 15.1 and happening in trunk:

```
#include <stdatomic.h>
#include <stdint.h>
typedef _Atomic(uintptr_t) g;
_Static_assert(_Generic(g(0)))
```

```
<source>:4:1: internal compiler error: Segmentation fault
    4 | _Static_assert(_Generic(g(0)))
      | ^~~~~~~~~~~~~~
0x261bc05 diagnostic_context::diagnostic_impl(rich_location*,
diagnostic_metadata const*, diagnostic_option_id, char const*, __va_list_tag
(*) [1], diagnostic_t)
        ???:0
0x2639976 internal_error(char const*, ...)
        ???:0
0xa2d7cb groktypename(c_type_name*, tree_node**, bool*)
        ???:0
0xab9b0e c_parse_file()
        ???:0
0xb38779 c_common_parse_file()
        ???:0
```

To reproduce quickly:

https://godbolt.org/z/a9eofno5j