Trigger postponed jobs on running_ec if that is available

	Currently, any postponed job triggered from a non-ruby thread gets sent
	to the main thread, but if the main thread is sleeping it won't be
	checking ints. Instead, we should try and interrupt running_ec if that's
	possible, and only fall back to the main thread if it's not.

	[Bug #20197]
	---
	 ractor.c | 16 ++++++++++++++++
	 1 file changed, 16 insertions(+)