Dear gsll-dev,
I was unable to build gsll (through quicklisp) on my gentoo box today because of "missing ffi.h". After I filled a bug report* with gentoo they gave me the advice to use
pkg-config --cflags-only-I libffi
to get the right path to ffi.
I am able to build gsll anyway but maybe this "tool" is something that could be incorporated into the build of gsll.
Cheers, Niklas