We have developed an alternate clang driver and placed it as open source in google code.
http://code.google.com/p/alternate-clang-driver/
Most people are using cross compilers for MIPS. We needed something different than what the clang driver provides us at this time.
This driver behaves enough like gcc cross drivers for us to run make files and other things meant for gcc right out of the box. We have for example run dejagnu gcc using it with no problems.
It's still in development but it works very well for us right now.
I intended to put more documentation for it before announcing it but our schedules are overloaded now and I can't assign anyone to do that for the next 2 months so I decided to just announce it now.
We can put resources into bug fixing and extensions but we already know how it works so it's not essential for us to do more docs at this time. 
It's a simple program and written in python and I think it's pretty easy to understand from just looking at the code.
We welcome other people to help make it work better for more platforms than just MIPS.