Revert "[CMake] Simplify CMake handling for zlib"

This quietly disabled use of zlib on Windows even when building with
-DLLVM_ENABLE_ZLIB=FORCE_ON.

> Rather than handling zlib handling manually, use find_package from CMake
> to find zlib properly. Use this to normalize the LLVM_ENABLE_ZLIB,
> HAVE_ZLIB, HAVE_ZLIB_H. Furthermore, require zlib if LLVM_ENABLE_ZLIB is
> set to YES, which requires the distributor to explicitly select whether
> zlib is enabled or not. This simplifies the CMake handling and usage in
> the rest of the tooling.
>
> This is a reland of abb00753 with all followup changes and fixes that
> should address issues that were reported in PR44780.
>
> Differential Revision: https://reviews.llvm.org/D79219

This reverts commit 10b1b4a2 and follow-ups
64d99cc6 and
f9fec044.