gdb: add program_space parameter to target_so_ops::clear_solib

gdb: add program_space parameter to target_so_ops::clear_solib

The clear_solib is implicitly meant to clear the resources associated to
the current program space (that's what the solib implementations that
actually support multi-program-space / multi-inferior do).  Make that
explicit by adding a program_space parameter and pass down
current_program_space in call sites.  The implementation of the
clear_solib callbacks is fairly simple, I don't think any of them rely
on global state other than accessing current_program_space.

Change-Id: I8d0cc4db7b4f8db8d7452879c0c62db03269bf46
Approved-By: Pedro Alves <pedro@palves.net>
Reviewed-By: Reviewed-By: Lancelot Six <lancelot.six@amd.com>