Probably the official package from llvm.org unless you use something like macports or homebrew. They should install under /usr/local.

So I went with homebrew which I think installs everything under /usr/local by default. Now I get:

Configuring dph-examples-0.6.1.3...

/var/folders/57/rjs423s5227dnc8rh_2rp4jh0000gn/T/95011.c:1:0:

internal compiler error: Illegal instruction: 4

Please submit a full bug report,

with preprocessed source if appropriate.

See <URL:http://developer.apple.com/bugreporter> for instructions.

cabal: Error: some packages failed to install:

dph-examples-0.6.1.3 failed during the configure step. The exception was:

ExitFailure 1