Wire up ability to print RTL program arities

Wire up ability to print RTL program arities

* libguile/procprop.c (scm_i_procedure_arity): Allow RTL programs to
  dispatch to scm_i_program_arity.

* libguile/programs.c (scm_i_program_print): Refactor reference to
  write-program.
  (scm_i_rtl_program_minimum_arity): New procedure, dispatches to
  Scheme.
  (scm_i_program_arity): Dispatch to scm_i_rtl_program_minimum_arity if
  appropriate.

* module/system/vm/debug.scm (program-minimum-arity): New export.

* module/system/vm/program.scm (rtl-program-minimum-arity): New internal
  function.
  (program-arguments-alists): New helper, implemented also for RTL
  procedures.
  (write-program): Refactor a bit, and call program-arguments-alists.

* test-suite/tests/rtl.test ("simply procedure arity"): Add tests that
  arities make it all the way to cold ELF and back to warm Guile.