Implement C _FloatN, _FloatNx types [version 6]

[Joseph Myers]

On Fri, 19 Aug 2016, Richard Biener wrote:

> Ok if libcpp maintainers do not object.

I consider the libcpp changes something I can self-approve - but, any 
comments?

> Can you quickly verify if LTO works with the new types?  I don't see anything
> that would prevent it but having new global trees and backends initializing them
> might come up with surprises (see tree-streamer.c:preload_common_nodes)

Well, the execution tests are in gcc.dg/torture, which is run with various 
options including -flto (and I've checked the testsuite logs to confirm 
these tests are indeed run with such options).  Is there something else 
you think should be tested?

-- 
Joseph S. Myers
joseph@codesourcery.com