Runtimes external project (compiler-rt / combined runtimes) reconfigures
with an initial cache that did not propagate `ZLIB_LIBRARY_RELEASE`.
CMake 4.x `FindZLIB` may leave `ZLIB_LIBRARY` unset while finding
headers, leading to:
```
-- Could NOT find ZLIB (missing: ZLIB_LIBRARY) (found version "...")
```
and later when loading LLVM exports from the main build:
```
The link interface of target "LLVMSupport" contains: ZLIB::ZLIB
but the target was not found.
```
This was found by building the Windows installer with:
```
llvm\utils\release\build_llvm_release.bat --x64 --version 23.0.0 --skip-checkout --local-python
```
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