The std::basic_stringbuf::get_allocator() member is only available for
the SSO std::string ABI.
libstdc++-v3/ChangeLog:
* testsuite/27_io/basic_istringstream/cons/char/string_view.cc:
Only check get_allocator() for new string ABI.
* testsuite/27_io/basic_ostringstream/cons/char/string_view.cc:
Likewise.
* testsuite/27_io/basic_stringbuf/cons/char/string_view.cc:
Likewise.
* testsuite/27_io/basic_stringstream/cons/char/string_view.cc:
Likewise.
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>