Add support for vrange streaming.

Add support for vrange streaming.

I think it's time for the ranger folk to start owning range streaming
instead of passes (IPA, etc) doing their own thing.  I have plans for
overhauling the IPA code later this cycle to support generic ranges,
and I'd like to start cleaning up the streaming and hashing interface.

This patch adds generic streaming support for vrange.

gcc/ChangeLog:

	* data-streamer-in.cc (streamer_read_real_value): New.
	(streamer_read_value_range): New.
	* data-streamer-out.cc (streamer_write_real_value): New.
	(streamer_write_vrange): New.
	* data-streamer.h (streamer_write_vrange): New.
	(streamer_read_value_range): New.