Fortran: Fix for class defined operators [PR99124].

Fortran: Fix for class defined operators [PR99124].

2021-02-23  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/99124
	* resolve.c (resolve_fl_procedure): Include class results in
	the test for F2018, C15100.
	* trans-array.c (get_class_info_from_ss): Do not use the saved
	descriptor to obtain the class expression for variables. Use
	gfc_get_class_from_expr instead.

gcc/testsuite/
	PR fortran/99124
	* gfortran.dg/class_defined_operator_2.f03 : New test.
	* gfortran.dg/elemental_result_2.f90 : New test.
	* gfortran.dg/class_assign_4.f90: Correct the non-conforming
	elemental function with an allocatable result with an operator
	interface with array dummies and result.

(cherry picked from commit 29a5298955f777c539c628f51e78b75d8e586c44)