gdb/solib: add solib -> solib_ops backlink The subsequent C++ification commit makes it so that one struct solib_ops is instantiated for each program space. For some operations, it will then become necessary to be able to get the right solib_ops instance from a given solib. Add an solib -> solib_ops backlink for that. Change-Id: Ib95407b3fa5fcfba55cf874e0e9dcd2d43a402e4 Approved-By: Pedro Alves <pedro@palves.net>