[Bug plugins/126882] New: [17 regression] -Wodr in callback-info.h vs plugin.cc

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126882

            Bug ID: 126882
           Summary: [17 regression] -Wodr in callback-info.h vs plugin.cc
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Keywords: build
          Severity: normal
          Priority: P3
         Component: plugins
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sjames at gcc dot gnu.org
  Target Milestone: ---

When building trunk with LTO, I see:
```
/var/tmp/portage.notmp/portage/sys-devel/gcc-17.0.9999/work/gcc-17.0.9999/gcc/callback-info.h:28:7:
warning: type ‘struct callback_info’ violates the C++ One Definition Rule
[-Wodr]
   28 | class callback_info
      |       ^
/var/tmp/portage.notmp/portage/sys-devel/gcc-17.0.9999/work/gcc-17.0.9999/gcc/plugin.cc:104:8:
note: a different type is defined in another translation unit
  104 | struct callback_info
      |        ^
/var/tmp/portage.notmp/portage/sys-devel/gcc-17.0.9999/work/gcc-17.0.9999/gcc/callback-info.h:36:12:
note: the first difference of corresponding definitions is field ‘fn_idx’
   36 |   unsigned fn_idx;
      |            ^
/var/tmp/portage.notmp/portage/sys-devel/gcc-17.0.9999/work/gcc-17.0.9999/gcc/plugin.cc:106:15:
note: a field with different name is defined in another translation unit
  106 |   const char *plugin_name;   /* Name of plugin that registers the
callback.  */
      |               ^
```