Relocate CMake target export definitions

Relocate CMake target export definitions

When exporting a CMake target the `install(TARGETS ${ZLIB_INSTALL_LIBRARIES})` is repeated with an `EXPORT` parameter. On Windows this would install the `.dll` files into the `lib` directory.

Set the `EXPORT_NAME` earlier and unconditionally on the `TARGET`. Then move the `EXPORT` to a single `install(TARGETS)`.