Introduce target_filesystem_is_local

Introduce target_filesystem_is_local

This commit introduces a new target method target_filesystem_is_local
which can be used to determine whether or not the filesystem accessed
by the target_fileio_* methods is the local filesystem.

gdb/ChangeLog:

	* target.h (struct target_ops) <to_filesystem_is_local>:
	New field.
	(target_filesystem_is_local): New macro.
	* target-delegates.c: Regenerate.
	* remote.c (remote_filesystem_is_local): New function.
	(init_remote_ops): Initialize to_filesystem_is_local.