ffcall vs libffi support

[Riccardo Mottola]

Hi,

while libffi is preferred on most platforms, we continue(d) to support 
ffcall. I use it for example on windows.

To do that, I used --enable-ffcall, which is still listed in the help .

I tried to reconfigure base:
...
checking use of fake-main definition... no
checking ffi.h usability... no
checking ffi.h presence... no
checking for ffi.h... no
checking callback.h usability... yes
checking callback.h presence... yes
checking for callback.h... yes
configure: WARNING: ffi support seems to be missing on this system ... 
please in
stall a recent libffi
checking for forwarding callback in runtime... yes
checking FFI library usage... none

did we we remove the support? or is something else broken?
I did not see any particular commit in base's configure that would break 
this.

Riccardo