clang requires a fairly modern [host compiler](http://llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library), so typically you will have to install a new one. The easiest thing to do is to just create a fresh build of GCC:
```
sudo apt-get install libgmp-dev libmpfr-dev libmpc-dev make build-essential libtool zip gcc-multilib autogen
sudo apt-get install libsqlite3-dev libgmp-dev libmpfr-dev libmpc-dev make build-essential libtool zip gcc-multilib autogen