Do not let internal JDK zlib symbols leak out of fastdebug libzip.so

[Martin Buchholz]

Hi Alan, Xueming, build-ers,

I'd like you to do a code review.

I've finally figured out why fastdebug jdk occasionally gives InternalError
in the zip code.

Exception in thread "main" java.lang.InternalError
at java.util.zip.Inflater.init(Native Method)
at java.util.zip.Inflater.<init>(Inflater.java:101)
at java.util.zip.ZipFile.getInflater(ZipFile.java:448)

It's because:
- jdk changed structure size of z_stream struct
- making jdk zlib incompatible with stock zlib
- as a result of which, it is imperative to keep jdk zlib sequestered from
system zlib
- so need to not export zlib symbols from libzip.so
- so need to tell makefiles to use linker script unconditionally

http://cr.openjdk.java.net/~martin/webrevs/openjdk8/hide-zlib/