Currently, when building gcc, building is disabled for zlib. If this is enabled, we can further the progress of the 64-bit windows target platform.
I think it is only disable because libjava support is disabled because libffi has not been ported yet. So really libffi support needs to be added and then libjava support can be added and in turn zlib can be enabled.
Now libffi is enabled and libjava can be enabled by configure switch.
gcc build libz only if libjava gets enabled. There is no need for gcc to build it without this target-library. YOu can enable now java built, then libz gets built too.