#648 widl does not support acf option

[tomrittervg]

Firefox passes the -acf option as shown here:
http://searchfox.org/mozilla-central/source/accessible/ipc/win/handler/Makefile.in#23

This option is not supported in widl:
https://sourceforge.net/p/mingw-w64/mingw-w64/ci/master/tree/mingw-w64-tools/widl/src/widl.c#l48

[Jacek Caban]

This is fixed now, widl supports -acf option.