Clang has several different versions available on MacPorts:
$ port search clang
clang @2.9 (lang)
C, C++, Objective C and Objective C++ compiler
clang-2.9 @2.9 (lang)
C, C++, Objective C and Objective C++ compiler
clang-3.0 @3.0 (lang)
C, C++, Objective C and Objective C++ compiler
clang-3.1 @3.1-r154872 (lang)
C, C++, Objective C and Objective C++ compiler
clang-devel @3.0 (lang)
C, C++, Objective C and Objective C++ compiler
clang_select @0.1 (sysutils)
common files for selecting default clang version
Found 6 ports.
, clang, 2.9. 3.1, clang-3.1. clang_select, , Clang; Clang, .