Fortran: deferred-length character optional dummy arguments [PR93762,PR100651]

gcc/fortran/ChangeLog:

	PR fortran/93762
	PR fortran/100651
	* trans-array.cc (gfc_trans_deferred_array): Add presence check
	for optional deferred-length character dummy arguments.
	* trans-expr.cc (gfc_conv_missing_dummy): The character length for
	deferred-length dummy arguments is passed by reference, so that
	its value can be returned.  Adjust handling for optional dummies.

gcc/testsuite/ChangeLog:

	PR fortran/93762
	PR fortran/100651
	* gfortran.dg/optional_deferred_char_1.f90: New test.