gdb: use gdb::unordered_{set,map} at a few places

gdb: use gdb::unordered_{set,map} at a few places

Use the gdb:: set/map types instead of the std:: ones.  I only changed
places in files I can build on my dev machine.

I needed to explicitly default the move constructor and assigment
operator in proc_mem_file.  I think this is ok, as nothing takes the
address of a proc_mem_file, requiring it not to move.

I also needed to do it for refcnt_fd, in solib-rocm.c.  It's a bit odd
to prevent moving / copying a refcnt_fd, as this struct doesn't directly
hold a resource, but I think I get why it was done.

Change-Id: If6f2d7ba3b1ae338eba38b0ab9f987400e661dff
Approved-By: Tom Tromey <tom@tromey.com>