Most header files use forward decl for union scm_vm_stack_element

* libguile.h: Add includes for frames.h and vm.h.  Probably need to
  revisit these includes.
* libguile/scm.h (struct scm_frame, union scm_vm_stack_element)
  (struct scm_vm): Add forward declarations.
* libguile/vm.h: Remove frames.h include.
* libguile/foreign.h:
* libguile/gsubr.h: Remove forward decls of union scm_vm_stack_element.
* libguile/control.c:
* libguile/eval.c:
* libguile/print.c: Add frames.h includes.
* libguile/threads.h: Remove continuations.h.
* libguile/vm.c: Add continuations.h.
* libguile/control.h: Swap vm.h include for scm.h include.
* libguile/continuations.h: Add programs.h include for SCM_PROGRAM_P.

libguile.h

@@ -58,6 +58,7 @@ extern "C" {
 #include "libguile/foreign.h"
 #include "libguile/foreign-object.h"
 #include "libguile/fports.h"
+#include "libguile/frames.h"
 #include "libguile/gc.h"
 #include "libguile/generalized-arrays.h"
 #include "libguile/generalized-vectors.h"
@@ -116,6 +117,7 @@ extern "C" {
 #include "libguile/vectors.h"
 #include "libguile/srfi-4.h"
 #include "libguile/version.h"
+#include "libguile/vm.h"
 #include "libguile/vports.h"
 #include "libguile/weak-set.h"
 #include "libguile/weak-table.h"

libguile/continuations.h

@@ -24,6 +24,7 @@
 
 #include <setjmp.h>
 
+#include "libguile/programs.h"
 #include "libguile/throw.h"
 
 

libguile/control.c

@@ -25,6 +25,7 @@
 
 #include "dynstack.h"
 #include "extensions.h"
+#include "frames.h"
 #include "gsubr.h"
 #include "instructions.h"
 #include "list.h"

libguile/control.h

@@ -22,7 +22,7 @@
 
 #include <setjmp.h>
 
-#include "libguile/vm.h"
+#include "libguile/scm.h"
 
 
 SCM_INTERNAL SCM scm_i_prompt_pop_abort_args_x (struct scm_vm *vp,

libguile/eval.c

@@ -37,6 +37,7 @@
 #include "eq.h"
 #include "expand.h"
 #include "feature.h"
+#include "frames.h"
 #include "fluids.h"
 #include "goops.h"
 #include "gsubr.h"

libguile/foreign.h

@@ -98,8 +98,6 @@ SCM_INTERNAL SCM scm_pointer_to_string (SCM pointer, SCM length, SCM encoding);
    arguments.
  */
 
-union scm_vm_stack_element;
-
 SCM_API SCM scm_pointer_to_procedure (SCM return_type, SCM func_ptr,
 				      SCM arg_types);
 SCM_API SCM scm_pointer_to_procedure_with_errno (SCM return_type, SCM func_ptr,

libguile/gsubr.h

@@ -55,7 +55,6 @@
 SCM_INTERNAL int scm_i_primitive_code_p (const uint32_t *code);
 SCM_INTERNAL uintptr_t scm_i_primitive_call_ip (SCM subr);
 
-union scm_vm_stack_element;
 SCM_INTERNAL SCM scm_apply_subr (union scm_vm_stack_element *sp,
                                  ptrdiff_t nargs);
 

libguile/print.c

@@ -41,6 +41,7 @@
 #include "eval.h"
 #include "fluids.h"
 #include "foreign.h"
+#include "frames.h"
 #include "goops.h"
 #include "gsubr.h"
 #include "hashtab.h"

libguile/scm.h

@@ -824,6 +824,9 @@ typedef struct scm_dynamic_state scm_t_dynamic_state;
 typedef struct scm_print_state scm_print_state;
 typedef struct scm_dynstack scm_t_dynstack;
 typedef int32_t scm_t_wchar;
+struct scm_frame;
+struct scm_vm;
+union scm_vm_stack_element;
 
 
 

libguile/threads.h

@@ -29,7 +29,6 @@
 #include "libguile/dynstack.h"
 #include "libguile/iselect.h"
 #include "libguile/smob.h"
-#include "libguile/continuations.h"
 #include "libguile/vm.h"
 
 #if SCM_USE_PTHREAD_THREADS

libguile/vm.c

@@ -41,6 +41,7 @@
 #include "atomics-internal.h"
 #include "bdw-gc.h"
 #include "cache-internal.h"
+#include "continuations.h"
 #include "control.h"
 #include "dynwind.h"
 #include "eval.h"

libguile/vm.h

@@ -21,7 +21,6 @@
 #define _SCM_VM_H_
 
 #include <libguile/gc.h>
-#include <libguile/frames.h>
 #include <libguile/programs.h>
 
 enum {