Part 1: Install llvm-gcc

$ sudo port install  llvm-gcc42
/opt/local/bin$ sudo ln -s llvm-gcc-4.2 llvm-gcc

Part 2: Install llvm
llvm-2.6$ ./configure --enable-optimized
llvm-2.6$ make

Part 3: Install KLEE
klee$ ./configure --with-llvm=/path/llvm-2.6
klee$ add -fexceptions flag in Makefile.common: CXX.Flags += -DKLEE_DIR=\"$(PROJ_OBJ_ROOT)\" -fexceptions
klee$ make
klee/Release/lib$ ln -s libkleeRuntimeIntrinsic.a libkleeRuntimeIntrinsic.bca

Part 4: Use KLEE
klee/examples/islower$ llvm-gcc -I../../include  --emit-llvm -c -g demo.c
klee/examples/islower$ ../../Release/bin/klee demo.o