freetype2, fontconfig: Fix Cygwin hosted build

For some reason, freetype and fontconfig need --build explicitly set on
the command line to correctly detect a cross compile from Cygwin to
MinGW.
libgpg_error: Prevent iconv from hanging on Cygwin

I have no idea why this works.
luajit: Fix cross to different bitness from Cygwin

luajit only supports cross compilation to architectures with the same
pointer width. This is hard on Cygwin, since it has no multilib
compilers, but luckily the target compilers can be used instead.
luajit: improve setting compiler flags

This should make things more robust with respect to 32-bit host
systems.