Getting perl scripting to work needs a few things:

 - configure with --with-perl-staticlib

 - libperl.dll is required in linking and running irssi, it's normally
   located somewhere around /usr/lib/perl5/5.6.1/cygwin/CORE/libperl5_6_1.dll
   copy it to eg. /usr/bin/libperl.dll

 - -DUSEIMPORTLIB is needed to be defined while compiling src/perl directory.
   It doesn't hurt to be defined everywhere, so configure irssi with:

     CFLAGS='-DUSEIMPORTLIB' ./configure --with-perl-staticlib