gdb: update gdb-gdb.py.in for latest changes to struct field

This commit updates uses of 'loc' and 'loc_kind' to 'm_loc' and
'm_loc_kind' respectively, in gdb-gdb.py.in, which is required after
this commit:

  commit cd3f655cc7a55437a05aa8e7b1fcc9051b5fe404
  Date:   Thu Sep 30 22:38:29 2021 -0400

      gdb: add accessors for field (and call site) location

I have also incorporated this change:

  https://sourceware.org/pipermail/gdb-patches/2021-September/182171.html

Which means we print 'm_name' instead of 'name' when displaying the
'm_name' member variable.

Finally, I have also added support for the new TYPE_SPECIFIC_INT
fields, which were added with this commit:

  commit 20a5fcbd5b28cca88511ac5a9ad5e54251e8fa6d
  Date:   Wed Sep 23 09:39:24 2020 -0600

      Handle bit offset and bit size in base types

I updated the gdb.gdb/python-helper.exp test to cover all of these
changes.