#2528 configure step partially(?) ignores `USE_SYSTEM_ZLIB:BOOL=OFF`.

[Hanspeter Niederstrasser]

On OS X, the system zlib is version 1.2.5, which does not have z_const. Part of the DviWare program uses z_const, so I disabled using the system-zlib in cmake to use the internal zlib-1.2.8. However, during the configure step, cmake still searches for and finds the system headers and libraries:

-- Found ZLIB: /usr/lib/libz.dylib (found version "1.2.5") 
// Use the system zlib compression library.
USE_SYSTEM_ZLIB:BOOL=OFF
// Path to a file.
ZLIB_INCLUDE_DIR:PATH=/usr/include
// Path to a library.
ZLIB_LIBRARY_RELEASE:FILEPATH=/usr/lib/libz.dylib

and then cmake configure fails:

CMake Error at Programs/DviWare/dvipdfm-x/CMakeLists.txt:296 (add_executable):
  Target "miktex-xdvipdfmx" links to target "MiKTeX::Imported::ZLIB" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?

If I don't disable system-zlib, configuring concludes correctly, and the build then fails later on with undeclared z_const.

[Hanspeter Niederstrasser]

For the completeness, here's the error if I try to use system-zlib-1.2.5:

cd /sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Programs/DviWare/dvipdfm-x && /sw/var/lib/fink/path-prefix-clang/cc  -DHAVE_CONFIG_H -DHAVE_FT2BUILD_H=1 -DHAVE_LIBFONTCONFIG=1 -DHAVE_LIBFREETYPE=1 -DHAVE_LIBPNG=1 -DHAVE_LIBZ=1 -DHAVE_ZLIB=1 -DHAVE_ZLIB_COMPRESS2=1 -DHAVE_ZLIB_H=1 -DMIKTEX -DMIKTEX_APP_SHARED -DMIKTEX_CORE_SHARED -DMIKTEX_KPSEMU_SHARED -DMIKTEX_MD5_SHARED -DMIKTEX_MPM_SHARED -DMIKTEX_TRACE_SHARED -DMIKTEX_UNIX -DMIKTEX_UTIL_SHARED -DXETEX -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Programs/DviWare/dvipdfm-x -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/UI/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/App/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Libraries/MiKTeX/Core/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/Core/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Libraries/3rd/md5/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/Trace/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/Util/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Libraries/MiKTeX/PackageManager/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/PackageManager/include -isystem /sw/include -isystem /sw/include/freetype2 -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/finkbuild/Libraries/MiKTeX/KPathSeaEmulation/include -I/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Libraries/MiKTeX/KPathSeaEmulation/include  -O3 -DNDEBUG -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk -mmacosx-version-min=10.11   -std=gnu99 -o CMakeFiles/miktex-xdvipdfmx.dir/source/pdfobj.c.o   -c /sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source/pdfobj.c
/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source/pdfobj.c:2183:17: error: use of undeclared identifier 'z_const'; did you
      mean 'const'?
  z.next_in  = (z_const Bytef *) data; z.avail_in  = len;
                ^~~~~~~
                const
/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source/pdfobj.c:2183:17: error: expected expression
/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source/pdfobj.c:2456:17: error: use of undeclared identifier 'z_const'; did you
      mean 'const'?
  z.next_in  = (z_const Bytef *) data; z.avail_in  = len;
                ^~~~~~~
                const
/sw/build.build/miktex-tools-2.9.6050-1/miktex-2.9-2016-09-10/Programs/DviWare/dvipdfm-x/source/pdfobj.c:2456:17: error: expected expression
4 errors generated.