How to compile FFmpeg with libfdkaac into a single static binary?
Thanks for stib's suggestion. I leave my answer here.

FFmepg build process take higher priority to use dynamic library even if static libraries are ready. Therefore, I first removed some external libraries support from build configuration and make sure all external libraries are only static (remove *.dylib from prefix /usr/local/lib). Then rebuild it with the following command:

./configure --pkg-config-flags="--static" --libdir=/usr/local/lib --extra-version=ntd_20150128 --disable-shared --enable-static --enable-gpl --enable-pthreads --enable-nonfree  --enable-libass --enable-libfdk-aac  --enable-libmp3lame  --enable-libx264 --enable-filters --enable-runtime-cpudetect


Remember to define --pkg-config-flags="--static", asking build process to use static library. Then, we will get a single executable FFmpeg binary!

P.S.: I removed the libass support from the configuration, because libass depends on Fontconfig lib which I only have dynamic library available. I'll put the libass support back once I figured out how to make a static library of fontconfig.

Thanks.