Fortran: deferred length of character variables shall not get lost [PR113911]

	PR fortran/113911

gcc/fortran/ChangeLog:

	* trans-array.cc (gfc_trans_deferred_array): Do not clobber
	deferred length for a character variable passed as dummy argument.

gcc/testsuite/ChangeLog:

	* gfortran.dg/allocatable_length_2.f90: New test.
	* gfortran.dg/bind_c_optional-2.f90: Enable deferred-length test.