Simplify compile_module cleanup

Simplify compile_module cleanup

This simplifies compile_module cleanup by removing the need to
explicitly free anything.  struct setup_sections_data is also cleaned
up a bit.

gdb/ChangeLog
2020-09-23  Tom Tromey  <tom@tromey.com>

	* compile/compile-object-run.c (do_module_cleanup)
	<~do_module_cleanup> :Remove.
	(do_module_cleanup): Update.
	* compile/compile-object-load.h (struct munmap_list): Add move
	assignment operator.
	<source_file>: Now a std::string.
	<munmap_list>: Rename.  No longer a pointer.
	* compile/compile-object-load.c (struct setup_sections_data): Add
	constructor.
	<setup_one_section>: Declare.
	<munmap_list>: Move earlier.
	<m_bfd>: New member.
	<m_last_size, m_last_section_first, m_last_prot,
	m_last_max_alignment>: Rename, add initializers where needed.
	(setup_sections_data::setup_one_section): Rename from
	setup_sections.  Update.
	(compile_object_load): Update.  Don't use bfd_map_over_sections.