Fortran: add SELECTED_LOGICAL_KIND

gcc/fortran/ChangeLog:
	* expr.cc (check_transformational): Add SELECTED_LOGICAL_KIND
	to allowed functions for Fortran 2023.
	* gfortran.h (GFC_ISYM_SL_KIND): New.
	* gfortran.texi: Mention SELECTED_LOGICAL_KIND.
	* intrinsic.cc (add_functions): Add SELECTED_LOGICAL_KIND.
	(gfc_intrinsic_func_interface): Allow it in initialization
	expressions.
	* intrinsic.h (gfc_simplify_selected_logical_kind): New proto.
	* intrinsic.texi: Add SELECTED_LOGICAL_KIND.
	* simplify.cc (gfc_simplify_selected_logical_kind): New
	function.
	* trans-decl.cc (gfc_build_intrinsic_function_decls): Initialize
	gfor_fndecl_sl_kind.
	* trans-intrinsic.cc (gfc_conv_intrinsic_sl_kind): New function.
	(gfc_conv_intrinsic_function): Call it for GFC_ISYM_SL_KIND.
	* trans.h (gfor_fndecl_sl_kind): New symbol.

gcc/testsuite/ChangeLog:

	* gfortran.dg/selected_logical_kind_1.f90: New test.
	* gfortran.dg/selected_logical_kind_2.f90: New test.
	* gfortran.dg/selected_logical_kind_3.f90: New test.
	* gfortran.dg/selected_logical_kind_4.f90: New test.

libgfortran/ChangeLog:

	* gfortran.map: Add _gfortran_selected_logical_kind.
	* intrinsics/selected_int_kind.f90: Add SELECTED_LOGICAL_KIND.