gdb/windows: replace bfd_map_over_sections with gdb_bfd_sections

Replace bfd_map_over_sections with iteration over gdb_bfd_sections.
Change core_process_module_section's signature to take a cpms_data
reference instead of a void pointer.

Change-Id: Ic4f9a12c9c1479799ec87658fd88490106b61836
Approved-By: Tom Tromey <tom@tromey.com>