Move pending addrmap globals to buildsym_compunit

Move pending addrmap globals to buildsym_compunit

This moves the pending addrmap-related globals into buildsym_compunit.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* buildsym.c (struct buildsym_compunit) <m_pending_addrmap,
	m_pending_addrmap_obstack, m_pending_addrmap_interesting>: New
	members.
	(pending_addrmap, pending_addrmap_obstack)
	(pending_addrmap_interesting): Remove.
	(scoped_free_pendings, record_block_range, make_blockvector)
	(prepare_for_building, reset_symtab_globals, buildsym_init):
	Update.