LuaJIT also does a lot less work for a given piece of code than LLVM. It generates relatively well optimized code for a dynamic language, but it doesn't do much of the low level optimizations that LLVM and GCC do.
Yes, that is how it usually goes, you exchange code performance for compiling performance but my point (a couple messages above) is that most of the time this performance is perfectly fine and it is only a tiny part of the codebase that may need the extra low level optimizations that LLVM and GCC can do (if it needs it at all). Of course this is a generality, the specifics depend on the project (chances are, the rendering parts of a CPU-based raytracer for CGI movies will need these optimizations much more than most projects, whereas a file manager most likely wont need them at all).