This has been already answered in the Apple developer forum, you can find the whole discussion in here. In the answer marked as the solution to the question they say:
1 – check your PATH variable first:
$ echo $PATH
2 – assuming /System/Library/Frameworks is not included in PATH, add it:
$ PATH=$PATH:/System/Library/Frameworks
3 -now we’re ready for Mr. Kochun’s incantation:
$ clang -fobjc-arc -framework Foundation main.m prog1