When I build --with-dffi=included everything builds fine. When I build --with-dffi=system I get the following build error: (sorry for those escape sequences, not sure why they are there, I bet there is some colorization going on somewhere, which is ironic since I am blind and it doesn't help me a bit).
dpp: /home/pi/ecl.git/src/c/ffi.d -> ffi.o.c [K/home/pi/ecl.git/src/c/ffi.d:218:4:[m[K [01;31m[Kerror: [m[K'[01m[Kffi_type_complex_float[m[K' undeclared here (not in a function); did you mean '[01m[Ksi_complex_float[m[K'? &[01;31m[Kffi_type_complex_float[m[K, /*@':csfloat',*/ [01;31m[K^~~~~~~~~~~~~~~~~~~~~~[m[K [32m[Ksi_complex_float[m[K [01m[K/home/pi/ecl.git/src/c/ffi.d:219:4:[m[K [01;31m[Kerror: [m[K'[01m[Kffi_type_complex_double[m[K' undeclared here (not in a function); did you mean '[01m[Kffi_type_longdouble[m[K'? &[01;31m[Kffi_type_complex_double[m[K, /*@':cdfloat',*/ [01;31m[K^~~~~~~~~~~~~~~~~~~~~~~[m[K [32m[Kffi_type_longdouble[m[K [01m[K/home/pi/ecl.git/src/c/ffi.d:220:4:[m[K [01;31m[Kerror: [m[K'[01m[Kffi_type_complex_longdouble[m[K' undeclared here (not in a function); did you mean '[01m[Kffi_type_longdouble[m[K'? &[01;31m[Kffi_type_complex_longdouble[m[K, /*@':clfloat',*/ [01;31m[K^~~~~~~~~~~~~~~~~~~~~~~~~~~[m[K [32m[Kffi_type_longdouble[m[K make[2]: *** [Makefile:88: ffi.o] Error 1 make[2]: Leaving directory '/home/pi/ecl.git/build/c' make[1]: *** [Makefile:144: libeclmin.a] Error 2 make[1]: Leaving directory '/home/pi/ecl.git/build' make: *** [Makefile:65: all] Error 2