Do not try to build LLVM with Zlib on Windows (#332)

CMake is accidentally picking up zlib from the CI environment, see actions/runner-images#6627 (comment), the build log now has this line:
```
  -- Found ZLIB: C:/Strawberry/c/lib/libz.a (found version "1.2.11") 
```

Disable zlib on Windows since we don't want the dependency there, this is also what Rust did a while back: rust-lang/rust#85762

llvm.proj

@@ -78,6 +78,7 @@
     <_LLVMBuildArgs Condition="'$(BuildOS)' == 'Windows_NT' and '$(Configuration)' == 'Release'" Include='-DLLVM_USE_CRT_RELEASE=MT' />
     <_LLVMBuildArgs Condition="'$(BuildOS)' == 'Windows_NT' and '$(Configuration)' == 'Debug'" Include='-DLLVM_USE_CRT_DEBUG=MTd' />
     <_LLVMBuildArgs Condition="'$(BuildOS)' == 'Windows_NT' and '$(Configuration)' == 'Debug'" Include='-DLLVM_USE_CRT_RELEASE=MTd' />
+    <_LLVMBuildArgs Condition="'$(BuildOS)' == 'Windows_NT'" Include='-DLLVM_ENABLE_ZLIB=OFF' />
   </ItemGroup>
 
   <ItemGroup>