Add "inferior" argument to some target_fileio functions

Add "inferior" argument to some target_fileio functions

This commit adds a new argument to all target_fileio functions with
filename arguments to allow the desired inferior to be specified.
This allows GDB to support systems where processes do not necessarily
share a common filesystem.

gdb/ChangeLog:

	* target.h (struct inferior): New forward declaration.
	(struct target_ops) <to_filesystem_is_local>: Update comment.
	(struct target_ops) <to_fileio_open>: New argument inf.
	Update comment.  All implementations updated.
	(struct target_ops) <to_fileio_unlink>: Likewise.
	(struct target_ops) <to_fileio_readlink>: Likewise.
	(target_filesystem_is_local): Update comment.
	(target_fileio_open): New argument inf.  Update comment.
	(target_fileio_unlink): Likewise.
	(target_fileio_readlink): Likewise.
	(target_fileio_read_alloc): Likewise.
	(target_fileio_read_stralloc): Likewise.
	* target.c (target_fileio_open): New argument inf.
	Pass inf to implementation.  Update debug printing.
	(target_fileio_unlink): Likewise.
	(target_fileio_readlink): Likewise.
	(target_fileio_read_alloc_1): New argument inf. Pass inf
	to target_fileio_open.
	(target_fileio_read_alloc): New argument inf. Pass inf to
	target_fileio_read_alloc_1.
	(target_fileio_read_stralloc): Likewise.
	* gdb_bfd.c (inferior.h): New include.
	(gdb_bfd_iovec_fileio_open): Replace unused "open_closure"
	argument with new argument "inferior".  Pass inferior to
	target_fileio_open.
	(gdb_bfd_open): Supply inferior argument to
	gdb_bfd_iovec_fileio_open.
	* linux-tdep.c (linux_info_proc): Supply inf argument to
	relevant target_fileio calls.
	(linux_find_memory_regions_full): Likewise.
	(linux_fill_prpsinfo): Likewise.
	* remote.c (remote_filesystem_is_local): Supply inf
	argument to remote_hostio_open.
	(remote_file_put): Likewise.
	(remote_file_get): Likewise.
	(remote_file_delete): Supply inf argument to
	remote_hostio_unlink.