Do not try to build LLVM with Zlib on Windows

We do not install Zlib on the CI but recent builds somehow started picking it's shared version.
To avoid relying on CI binaries so let's explicitly disable it.

src/bootstrap/native.rs

@@ -181,7 +181,7 @@ impl Step for Llvm {
             .define("LLVM_TARGET_ARCH", target_native.split('-').next().unwrap())
             .define("LLVM_DEFAULT_TARGET_TRIPLE", target_native);
 
-        if target != "aarch64-apple-darwin" {
+        if target != "aarch64-apple-darwin" && !target.contains("windows") {
             cfg.define("LLVM_ENABLE_ZLIB", "ON");
         } else {
             cfg.define("LLVM_ENABLE_ZLIB", "OFF");