* callback.c (os_stat): Make 3rd arg a host struct stat ptr.

	* callback.c (os_stat): Make 3rd arg a host struct stat ptr.
	(os_fstat): Likewise.  Validate fd argument.
	(cb_host_to_target_stat): Delete big_p arg.  If HS arg is NULL,
	just compute target stat struct length.
	* syscall.c: #include "libiberty.h", <sys/types.h>, <sys/stat.h>.
	(ENOSYS,ENAMETOOLONG): Provide definitions if missing.
	(get_string): Return host errno values so they can be properly
	translated later.
	(cb_syscall): Likewise.
	(cb_syscall, cases open,unlink): Use get_path instead of get_string.
	(cb_syscall, case read): Use read_stdin for file descriptor 0.
	(cb_syscall, case write): Use write_stderr for file descriptor 2.
	(cb_syscall): Add cases for lseek, unlink, stat, fstat, time.
	(get_path): New function.