Separate the Android build stuff from the upstream zlib stuff.

Another step towards a script that does the zlib upgrades for us...

Change-Id: I940b5b4e79d2a8daf7a47129bbea7bdaffd4140c
Upgrade to zlib 1.2.8.

From the upstream ChangeLog:

  Changes in 1.2.8 (28 Apr 2013)
  - Update contrib/minizip/iowin32.c for Windows RT [Vollant]
  - Do not force Z_CONST for C++
  - Clean up contrib/vstudio [Ro§]
  - Correct spelling error in zlib.h
  - Fix mixed line endings in contrib/vstudio

  Changes in 1.2.7.3 (13 Apr 2013)
  - Fix version numbers and DLL names in contrib/vstudio/*/zlib.rc

  Changes in 1.2.7.2 (13 Apr 2013)
  - Change check for a four-byte type back to hexadecimal
  - Fix typo in win32/Makefile.msc
  - Add casts in gzwrite.c for pointer differences

  Changes in 1.2.7.1 (24 Mar 2013)
  - Replace use of unsafe string functions with snprintf if available
  - Avoid including stddef.h on Windows for Z_SOLO compile [Niessink]
  - Fix gzgetc undefine when Z_PREFIX set [Turk]
  - Eliminate use of mktemp in Makefile (not always available)
  - Fix bug in 'F' mode for gzopen()
  - Add inflateGetDictionary() function
  - Correct comment in deflate.h
  - Use _snprintf for snprintf in Microsoft C
  - On Darwin, only use /usr/bin/libtool if libtool is not Apple
  - Delete "--version" file if created by "ar --version" [Richard G.]
  - Fix configure check for veracity of compiler error return codes
  - Fix CMake compilation of static lib for MSVC2010 x64
  - Remove unused variable in infback9.c
  - Fix argument checks in gzlog_compress() and gzlog_write()
  - Clean up the usage of z_const and respect const usage within zlib
  - Clean up examples/gzlog.[ch] comparisons of different types
  - Avoid shift equal to bits in type (caused endless loop)
  - Fix unintialized value bug in gzputc() introduced by const patches
  - Fix memory allocation error in examples/zran.c [Nor]
  - Fix bug where gzopen(), gzclose() would write an empty file
  - Fix bug in gzclose() when gzwrite() runs out of memory
  - Check for input buffer malloc failure in examples/gzappend.c
  - Add note to contrib/blast to use binary mode in stdio
  - Fix comparisons of differently signed integers in contrib/blast
  - Check for invalid code length codes in contrib/puff
  - Fix serious but very rare decompression bug in inftrees.c
  - Update inflateBack() comments, since inflate() can be faster
  - Use underscored I/O function names for WINAPI_FAMILY
  - Add _tr_flush_bits to the external symbols prefixed by --zprefix
  - Add contrib/vstudio/vc10 pre-build step for static only
  - Quote --version-script argument in CMakeLists.txt
  - Don't specify --version-script on Apple platforms in CMakeLists.txt
  - Fix casting error in contrib/testzlib/testzlib.c
  - Fix types in contrib/minizip to match result of get_crc_table()
  - Simplify contrib/vstudio/vc10 with 'd' suffix
  - Add TOP support to win32/Makefile.msc
  - Suport i686 and amd64 assembler builds in CMakeLists.txt
  - Fix typos in the use of _LARGEFILE64_SOURCE in zconf.h
  - Add vc11 and vc12 build files to contrib/vstudio
  - Add gzvprintf() as an undocumented function in zlib
  - Fix configure for Sun shell
  - Remove runtime check in configure for four-byte integer type
  - Add casts and consts to ease user conversion to C++
  - Add man pages for minizip and miniunzip
  - In Makefile uninstall, don't rm if preceding cd fails
  - Do not return Z_BUF_ERROR if deflateParam() has nothing to write

Change-Id: Ic05676d0ac8c877ba538ce60891d92472b73bf98