fix(nvvm): fix broken LLVM 7 download URL in build.rs

The tag name on GitHub was lowercase 'llvm-7.1.0', but the URL was hardcoded to use uppercase 'LLVM-7.1.0', which has no release assets.

Also added an explicit HTTP response code check to catch download failures early with a descriptive error message instead of failing later with an 'UnexpectedEof' during archive unpacking.

Author: Snehal-Reddy

crates/rustc_codegen_nvvm/build.rs

@@ -11,7 +11,7 @@ use tar::Archive;
 use xz::read::XzDecoder;
 
 static PREBUILT_LLVM_URL_LLVM7: &str =
-    "https://github.com/rust-gpu/rustc_codegen_nvvm-llvm/releases/download/LLVM-7.1.0/";
+    "https://github.com/rust-gpu/rustc_codegen_nvvm-llvm/releases/download/llvm-7.1.0/";
 
 fn main() {
     rustc_llvm_build(llvm19_enabled());
@@ -181,6 +181,13 @@ fn find_llvm_config_llvm7(target: &str) -> PathBuf {
             .expect("Failed to download prebuilt LLVM");
     }
 
+    let response_code = easy.response_code().unwrap();
+    if response_code != 200 {
+        fail(&format!(
+            "Failed to download prebuilt LLVM from {url}. HTTP response code: {response_code}"
+        ));
+    }
+
     let decompressor = XzDecoder::new(xz_encoded.as_slice());
     let mut ar = Archive::new(decompressor);