[Bug go/125701] New: configure checks for unordered_map but GCC requires C++11 already

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125701

            Bug ID: 125701
           Summary: configure checks for unordered_map but GCC requires
                    C++11 already
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

>From configure.ac:
```
AC_CHECK_HEADERS(unordered_map)
AC_CHECK_HEADERS(tr1/unordered_map)
AC_CHECK_HEADERS(ext/hash_map)
```

These used in go/go-system.h:
```
#if defined(HAVE_UNORDERED_MAP)
```

This can be removed and just include unordered_map/unordered_set
unconditionally.