Extra machine modes out of tm.h

[Mark Mitchell]

> Having separate files for just this thingy is IMO unnecessary
> complexity and hurts maintainability.  I think you should be
> able to dig out the EXTRA_CC_MODES from the port .h files as
> part of the configure process, with no change in the ports.

I disagree.

Having a separate file like this seems clearer to me.  These bits are
like "cp-tree.def"; an extension to a list of existing nodes.  Also,
if you generate these at configure time then when you add a mode
(admittedly almost never) you have to rerun configure.

The patch is OK for the mainline, assuming testing goes OK and that
you honor Joseph's request regarding sourcebuild.texi.

Thanks,

-- 
Mark Mitchell                mark@codesourcery.com
CodeSourcery, LLC            http://www.codesourcery.com