subrs are now VM trampoline procedures

subrs are now VM trampoline procedures

* libguile/_scm.h: Add foreign.h and programs.h to the private include
  list, as snarfing subrs with static allocation now needs access to
  some of their enums and macros.

* libguile/gsubr.c (create_gsubr): Instead of creating a tc7_gsubr
  object, create a VM program with the call-subr opcode, so that the
  representation of subrs is now gsubrs. CPP and elisp, together at
  last.
  (scm_subr_objcode_trampoline): New function, used by the SCM_DEFINE
  snarf macro.

* libguile/gsubr.h (SCM_SUBR_META_INFO, SCM_SUBR_PROPS)
  (SCM_SET_SUBR_GENERIC_LOC, SCM_SUBR_ARITY_TO_TYPE): Remove these
  macros. They were never deprecated, but hopefully people aren't using
  them.
  (SCM_SUBRF, SCM_SUBR_NAME, SCM_SUBR_GENERIC, SCM_SET_SUBR_GENERIC):
  Update to work on the new subr representation.

* libguile/objcodes.h (SCM_F_OBJCODE_IS_STATIC): New flag, indicates
  that the "backing store" of the objcode is statically allocated.

* libguile/procprop.c (scm_sym_name): Define here instead of in gsubr.c.

* libguile/snarf.h (SCM_DEFINE): If we are doing static allocation,
  statically allocate the foreign object, the object table, and the
  program, and use some SCM_SNARF_INITtery to fix things up.
  Unfortunately I have not been able to make this immutable. It might be
  possible, though.
  (SCM_IMMUTABLE_CELL, SCM_STATIC_DOUBLE_CELL, SCM_IMMUTABLE_FOREIGN):
  (SCM_STATIC_SUBR_OBJVECT, SCM_STATIC_PROGRAM): New helper macros.