Expose `rb_fiber_transfer` and `rb_fiber_transfer_kw`.

cont.c

@@ -2500,7 +2500,7 @@ rb_fiber_m_resume(int argc, VALUE *argv, VALUE fiber)
     return rb_fiber_resume_kw(fiber, argc, argv, rb_keyword_given_p());
 }
 
-static VALUE rb_fiber_transfer_kw(VALUE fiber_value, int argc, VALUE *argv, int kw_splat);
+VALUE rb_fiber_transfer_kw(VALUE fiber_value, int argc, const VALUE *argv, int kw_splat);
 
 /*
  *  call-seq:
@@ -2704,8 +2704,8 @@ rb_fiber_m_transfer(int argc, VALUE *argv, VALUE fiber_value)
     return rb_fiber_transfer_kw(fiber_value, argc, argv, rb_keyword_given_p());
 }
 
-static VALUE
-rb_fiber_transfer_kw(VALUE fiber_value, int argc, VALUE *argv, int kw_splat)
+VALUE
+rb_fiber_transfer_kw(VALUE fiber_value, int argc, const VALUE *argv, int kw_splat)
 {
     rb_fiber_t *fiber = fiber_ptr(fiber_value);
     if (RTEST(fiber->resuming_fiber)) {

include/ruby/internal/intern/cont.h

@@ -28,13 +28,18 @@ RBIMPL_SYMBOL_EXPORT_BEGIN()
 
 /* cont.c */
 VALUE rb_fiber_new(rb_block_call_func_t, VALUE);
-VALUE rb_fiber_resume(VALUE fib, int argc, const VALUE *argv);
-VALUE rb_fiber_resume_kw(VALUE fib, int argc, const VALUE *argv, int kw_splat);
-VALUE rb_fiber_yield(int argc, const VALUE *argv);
-VALUE rb_fiber_yield_kw(int argc, const VALUE *argv, int kw_splat);
 VALUE rb_fiber_current(void);
 VALUE rb_fiber_alive_p(VALUE);
 
+VALUE rb_fiber_resume(VALUE fiber, int argc, const VALUE *argv);
+VALUE rb_fiber_resume_kw(VALUE fiber, int argc, const VALUE *argv, int kw_splat);
+
+VALUE rb_fiber_yield(int argc, const VALUE *argv);
+VALUE rb_fiber_yield_kw(int argc, const VALUE *argv, int kw_splat);
+
+VALUE rb_fiber_transfer(VALUE fiber, int argc, const VALUE *argv);
+VALUE rb_fiber_transfer_kw(VALUE fiber, int argc, const VALUE *argv, int kw_splat);
+
 RBIMPL_SYMBOL_EXPORT_END()
 
 #endif /* RBIMPL_INTERN_CONT_H */