PR 44292 Handle large record lengths

PR 44292 Handle large record lengths

Now that the ABI supports large record lengths, there's a few places
in libgfortran where we need to use larger types. For internal units
which by definition are in-memory, it's enought to use ptrdiff_t, for
external units gfc_offset.

Regtested on x86_64-pc-linux-gnu?

libgfortran/ChangeLog:

2017-11-19  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/44292
	* io/transfer.c (skip_record): Use gfc_offset to handle large
	records.
	(next_record_r): Likewise.
	(sset): Likewise.
	(next_record_w): Use gfc_offset/ptrdiff_t appropriately.

From-SVN: r254918