PR libfortran/20179

	* io/unix.c (is_preconnected): Add function to test if a stream
	corresponds to a preconnected unit.
	* io/io.h: Add prototype for is_preconnected.
	* io/transfer.c (data_transfer_init): Do not truncate
	preconnected units.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@104141 138bc75d-0d04-0410-961f-82ee72b054a4