* bfd-target.c: Don't include gdb_assert.h or gdb_string.h.

	* bfd-target.c: Don't include gdb_assert.h or gdb_string.h.
	Include exec.h.
	(struct section_closure): Delete.
	(add_to_section_table): Delete.
	(build_target_sections_from_bfd): Delete.
	(target_bfd_xfer_partial): Use section_table_xfer_memory_partial.
	(target_bfd_reopen): Use build_section_table.
	* exec.c (xfer_memory): Move most code except for overlay
	debugging support from here...
	(section_table_xfer_memory): ... to this new function.
	(section_table_xfer_memory_partial): New.
	* exec.h (section_table_xfer_memory_partial): Declare.
	* bfd-target.h (build_target_sections_from_bfd): Delete
	declaration.