AC_FC_RECL_UNIT
When opening a file for direct access, you must specify
the record length with the OPEN specifier
RECL; however in the case of unformatted
direct access files, the units of this specifier
are processor dependent, and may be words or bytes. This
macro determines the units and defines
FC_RECL_UNIT to contain the number of bytes
(1, 2, 4, 8, ...) in the processor's unit of measurement.
Note that unformatted files are not themselves portable, and should only be used as either temporary files, or as data files which will be read by a program or library compiled with the same Fortran processor. With this macro, however, you can read and write such files in a portable way.