Build using clang

[shane-kerr]

Someone has requested a port of the MintCoin wallet to OpenBSD. Unfortunately modern gcc does not work on OpenBSD. I have filed bugs against gcc, but it does not look like it will get fixed by the gcc team anytime soon. I talked one of the OpenBSD developers and was told that there are compiler hardening techniques that need to be done to compilers before OpenBSD will use it.

It seems like an easier path for MintCoin is to get the wallet to build using clang, the LLVM C compiler, which is what most freedom-hating systems like BSD use.

This would also have the benefit of flushing out bugs in the code, as well as allowing static-error checking from clang as well.