Use sftp_realpath if no native realpath.

configure.ac

@@ -1783,6 +1783,7 @@ AC_CHECK_FUNCS([ \
 	raise \
 	readpassphrase \
 	reallocarray \
+	realpath \
 	recvmsg \
 	recallocarray \
 	rresvport_af \

openbsd-compat/bsd-misc.h

@@ -182,4 +182,8 @@ int flock(int, int);
 struct tm *localtime_r(const time_t *, struct tm *);
 #endif
 
+#ifndef HAVE_REALPATH
+#define realpath(x, y)	(sftp_realpath((x), (y))
+#endif
+
 #endif /* _BSD_MISC_H */