Fix ICE in trans_associate_var

2020-03-05  Paul Thomas  <pault@gcc.gnu.org>

	Backport from trunk
	PR fortran/92976
	* match.c (select_type_set_tmp): Variable 'selector' to replace
	select_type_stack->selector. If the selector array spec has
	explicit bounds, make the temporary's bounds deferred.

2020-03-05  Paul Thomas  <pault@gcc.gnu.org>

	Backport from trunk
	PR fortran/92976
	* gfortran.dg/select_type_48.f90 : New test.