solib-svr4: Pass down svr4_info as much as possible

solib-svr4: Pass down svr4_info as much as possible

While reviewing

  https://sourceware.org/ml/gdb-patches/2019-04/msg00141.html

I noticed that we relied heavily on global state through the
get_svr4_info function, which uses current_program_space.  I thought we
could improve this (make things more explicit and easier to follow) by

- Making get_svr4_info accept a program_space parameter, making it
  return the SVR4 info for that program space.
- Passing down the svr4_info object from callers as much as possible.

This means looking up the svr4_info for the appropriate program space at
the entry points of the solib-svr4.c file and passing it down.  For now,
these entry points (most of them are "methods" of svr4_so_ops) rely on
current_program_space, but we can later try to change the target_so_ops
interface to pass down the program space.

gdb/ChangeLog:

	* solib-svr4.c (get_svr4_info): Add pspace parameter.
	(svr4_keep_data_in_core): Pass current_program_space to get_svr4_info.
	(open_symbol_file_object): Likewise.
	(svr4_default_sos): Add info parameter.
	(svr4_read_so_list): Likewise.
	(svr4_current_sos_direct): Adjust functions calls to pass down
	info.
	(svr4_current_sos_1): Add info parameter.
	(svr4_current_sos): Call get_svr4_info, pass info down to
	svr4_current_sos_1.
	(svr4_fetch_objfile_link_map): Pass objfile->pspace to
	get_svr4_info.
	(svr4_in_dynsym_resolve_code): Pass current_program_space to
	get_svr4_info.
	(probes_table_htab_remove_objfile_probes): Pass objfile->pspace
	to get_svr4_info.
	(probes_table_remove_objfile_probes): Likewise.
	(register_solib_event_probe): Add info parameter.
	(solist_update_incremental): Pass info parameter down to
	svr4_read_so_list.
	(disable_probes_interface): Add info parameter.
	(svr4_handle_solib_event): Pass current_program_space to
	get_svr4_info.  Adjust disable_probes_interface cleanup.
	(svr4_create_probe_breakpoints): Add info parameter, pass it
	down to register_solib_event_probe.
	(svr4_create_solib_event_breakpoints): Add info parameter,
	pass it down to svr4_create_probe_breakpoints.
	(enable_break): Pass info down to
	svr4_create_solib_event_breakpoints.
	(svr4_solib_create_inferior_hook): Pass current_program_space to
	get_svr4_info.
	(svr4_clear_solib): Likewise.