Fortran: do not pass hidden character length for TYPE(*) dummy [PR110825]

gcc/fortran/ChangeLog:

	PR fortran/110825
	* gfortran.texi: Clarify argument passing convention.
	* trans-expr.cc (gfc_conv_procedure_call): Do not pass the character
	length as hidden argument when the declared dummy argument is
	assumed-type.

gcc/testsuite/ChangeLog:

	PR fortran/110825
	* gfortran.dg/assumed_type_18.f90: New test.