Adding `GC.compact` and compacting GC support.

This commit adds the new method `GC.compact` and compacting GC support.
Please see this issue for caveats:

  https://bugs.ruby-lang.org/issues/15626

[Feature #15626]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67479 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 0 deletions

diff --git a/symbol.h b/symbol.h
index 56568a91fc..3b9866d80f 100644
--- a/symbol.h
+++ b/symbol.h
@@ -54,6 +54,13 @@ id_type(ID id)
 
 typedef uint32_t rb_id_serial_t;
 
+typedef struct {
+    rb_id_serial_t last_id;
+    st_table *str_sym;
+    VALUE ids;
+    VALUE dsymbol_fstr_hash;
+} rb_symbols_t;
+
 static inline rb_id_serial_t
 rb_id_to_serial(ID id)
 {