hash.c: make rb_hash_keys extern

* hash.c (rb_hash_keys): make an internal public function.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45856 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

hash.c

@@ -1756,7 +1756,7 @@ keys_i(VALUE key, VALUE value, VALUE ary)
  *
  */
 
-static VALUE
+VALUE
 rb_hash_keys(VALUE hash)
 {
     VALUE keys;

internal.h

@@ -596,6 +596,7 @@ void rb_gc_resurrect(VALUE ptr);
 /* hash.c */
 struct st_table *rb_hash_tbl_raw(VALUE hash);
 #define RHASH_TBL_RAW(h) rb_hash_tbl_raw(h)
+VALUE rb_hash_keys(VALUE hash);
 VALUE rb_hash_values(VALUE hash);
 #define HASH_DELETED  FL_USER1
 #define HASH_PROC_DEFAULT FL_USER2