Make rda native-only

[Nathanael Nerode]

>Yes, please.  You forgot to explain what kind of error you're running
>into.  I've been building rda in a cross build environment pretty much
>daily.

Next time I'm feeling masochistic, I'll get you the exact errors.  It 
has to build *all* the host stuff first, so it takes hours, and 
I have to have a separate source tree (since I can't do any actual 
development with rda in my tree) so it takes a lot of disk space.

The executive summary is that the 'configure' script for rda either 
can't find the (newly built) cross gcc, or rejects CC as 'not 
working'.  God only knows why.