* CMake: 3rdParty/zlib fixes
1. zlib already provides a CMakeLists.txt, use it.
2. Stub find_package for source build. ZLIB is used by libpng via `find_package(ZLIB)`.
3. amiga.cmake: Remove `find_package(ZLIB)`.
* Update UWP build directory for zlibstatic.lib
Co-authored-by: staphen <staphen@gmail.com>