Create external names with or without trailing underscores.
–ext_names=plain: Do not add trailing underscore.
–ext_names=underscores: Add trailing underscore.
An external name is a name of a subroutine, function, block data subprogram, or labeled common. This option affects both the name of the routine’s entry point and the name used in calls to it. Use this flag to allow Fortran 95 routines to call (and be called by) other programming language routines.