[gdb/testsuite] Handle address class annotation for s390x in some test-cases

On s390x-linux, I ran into:
...
(gdb) ptype crash^M
type = class crash {^M
^M
  public:^M
    crash(int (class {...}::*)(class {...} * const @mode32));^M
}^M
(gdb) FAIL: gdb.dwarf2/dw2-anon-mptr.exp: ptype crash
...

The problem is that the test-case doesn't expect the address class annotation
@mode32.

The test-case uses a .S file, with the address size hard-coded to 4 bytes, and
that's something that is annotated with @mode32 on s390x (which uses 8 byte
addresses).

Fix this by allowing the annotation in the regexp.

Likewise in two other test-cases.

Tested on s390-linux and x86_64-linux.