[MacRuby-devel] About rake, llvm_config and "prefix"

Greetings All, I was trying to build MacRuby. However, I got an error saying that: The llvm-config executable was not located as /usr/local/bin/llvm-config. Please make sure LLVM is correctly installed on your machine and pass the llvm_config option to rake if necessary. I do have llvm 2.8 installed but resides a directory other than /usr/local/bin/. How may I tell rake to search for it? What exact command shall I type? BTW, is it possible to tell something like a "prefix" to rake when we want to install MacRuby into a specific path? Thanks, Huahang