PR libfortran/20179
	* io/unix.c (flush_if_preconnected): New function.
	* io/io.h: Add prototype for flush_if_preconnected.
	* io/transfer.c (data_transfer_init): Use flush_if_preconnected
	to workaround buggy mixed C-Fortran code.

	* gfortran.dg/mixed_io_1.f90: New test.
	* gfortran.dg/mixed_io_1.c: New file.

From-SVN: r106017