[LLVMdev] using just llvm/clang for building mips llvm

[reed kotler]

In case anyone is interested....

We don't need to compile llvm/clang using gcc anymore for the building 
of mips hosted llvm compilers.

We build a linux mips hosted compiler starting with llvm/clang on x86 
linux using the normal configure scripts and
then can use that resulting compiler to build further llvm/clang native 
compilers on the mips linux host.

The cross compiler and native compiler driver for Mips works seamlessly 
(thanks to Simon Atanasyan) just as gcc does.

For our build slave that is connected to the llvm build bots, we are 
using our native clang/llvm (built as above) to built the llc
that is used for make check.

I'm doing some more work to automate the testing of the recursed 
compilers and other verification on the mips target.