[DO NOT MERGE][CMake] Try to FORCE_ON zlib and zstd in LLVM

[guitargeek]

This is just to confirm/show that the builtin LLVM can't pick up the builtin zlib/zstd.

FYI @hageboeck, that's a useful datapoint when reviewing #22604 I hope

[guitargeek]

This PR successfully confirmed that neither the builtin_zstd nor builtin_zlib can be found by LLVM.

The alma10 arm64 (builtin_zlib=ON, builtin_zstd=ON) fails at find_package(zlib):

Call Stack (most recent call first):
  interpreter/llvm-project/llvm/CMakeLists.txt:8 (include)


CMake Error at interpreter/llvm-project/llvm/cmake/config-ix.cmake:180 (message):
  Failed to configure zlib
Call Stack (most recent call first):
  interpreter/llvm-project/llvm/CMakeLists.txt:981 (include)

And macOS 26 (builtin_zlib=OFF, builtin_zstd=ON) fails at find_package(zstd):

Call Stack (most recent call first):
  interpreter/llvm-project/llvm/CMakeLists.txt:8 (include)


CMake Error at interpreter/llvm-project/llvm/cmake/config-ix.cmake:193 (message):
  Failed to configure zstd, but LLVM_ENABLE_ZSTD is FORCE_ON
Call Stack (most recent call first):
  interpreter/llvm-project/llvm/CMakeLists.txt:981 (include)

[github-actions]

Test Results

    14 files      14 suites   2d 4h 13m 7s ⏱️
 3 844 tests  3 844 ✅ 0 💤 0 ❌
47 810 runs  47 810 ✅ 0 💤 0 ❌

Results for commit 2ec934b.

♻️ This comment has been updated with latest results.