[Feature #20470] Split GC into gc_impl.c

This commit splits gc.c into two files:

- gc.c now only contains code not specific to Ruby GC. This includes
  code to mark objects (which the GC implementation may choose not to
  use) and wrappers for internal APIs that the implementation may need
  to use (e.g. locking the VM).

- gc_impl.c now contains the implementation of Ruby's GC. This includes
  marking, sweeping, compaction, and statistics. Most importantly,
  gc_impl.c only uses public APIs in Ruby and a limited set of functions
  exposed in gc.c. This allows us to build gc_impl.c independently of
  Ruby and plug Ruby's GC into itself.

1 files changed, 3 insertions, 4 deletions

diff --git a/vm_core.h b/vm_core.h
index 3c656ff49d..8bec674963 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -609,10 +609,9 @@ typedef struct rb_at_exit_list {
     struct rb_at_exit_list *next;
 } rb_at_exit_list;
 
-struct rb_objspace;
-struct rb_objspace *rb_objspace_alloc(void);
-void rb_objspace_free(struct rb_objspace *);
-void rb_objspace_call_finalizer(struct rb_objspace *);
+void *rb_objspace_alloc(void);
+void rb_objspace_free(void *objspace);
+void rb_objspace_call_finalizer(void);
 
 typedef struct rb_hook_list_struct {
     struct rb_event_hook_struct *hooks;