Move 32-bit compat support for FIODGNAME to the right place.

ioctl(2) commands only have meaning in the context of a file descriptor
so translating them in the syscall layer is incorrect.

The new handler users an accessor to retrieve/construct a pointer from
the last member of the passed structure and relies on type punning to
access the other member which requires no translation.

Unlike r339174 this change supports both places FIODGNAME is handled.

Reviewed by:	kib
Obtained from:	CheriBSD
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D17475

newlib/libc/sys/rtems/include/sys/filio.h

@@ -63,4 +63,16 @@ struct fiodgname_arg {
 #define	FIOSEEKDATA	_IOWR('f', 97, off_t)	/* SEEK_DATA */
 #define	FIOSEEKHOLE	_IOWR('f', 98, off_t)	/* SEEK_HOLE */
 
+#ifdef _KERNEL
+#ifdef COMPAT_FREEBSD32
+struct fiodgname_arg32 {
+	int		len;
+	uint32_t	buf;	/* (void *) */
+};
+#define	FIODGNAME_32	_IOC_NEWTYPE(FIODGNAME, struct fiodgname_arg32)
+#endif
+
+void	*fiodgname_buf_get_ptr(void *fgnp, u_long com);
+#endif
+
 #endif /* !_SYS_FILIO_H_ */