Fix s390x compatibility.
* gdb.dwarf2/pr11465.S (DW_TAG_pointer_type): Use PTRBITS. Twice.
* gdb.dwarf2/pr11465.exp: Set ptrbits, use it for -DPTRBITS.
* gdb.dwarf2/pr11465.exp: New test.
* gdb.dwarf2/pr11465.S: New file.
* gdb.dwarf2/dw2-double-set-die-type.S: New file.
* gdb.dwarf2/dw2-double-set-die-type.exp: New test.