Fortran: Fix some select rank issues [PR97694 and 97723].

Fortran: Fix some select rank issues [PR97694 and 97723].

2020-12-27  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/97694
	PR fortran/97723
	* check.c (allocatable_check): Select rank temporaries are
	permitted even though they are treated as associate variables.
	* resolve.c (gfc_resolve_code): Break on select rank as well as
	select type so that the block os resolved.
	* trans-stmt.c (trans_associate_var): Class associate variables
	that are optional dummies must use the backend_decl.

gcc/testsuite/
	PR fortran/97694
	PR fortran/97723
	* gfortran.dg/select_rank_5.f90: New test.