Check LLVM_HOME when build

build.rs

@@ -85,11 +85,17 @@ fn gen_flutter_rust_bridge() {
             .output()
             .expect("failed to execute flutter pub get");
     };
-    
     let llvm_path = match std::env::var("LLVM_HOME") {
-        Ok(path) => Some(vec![path]),
-        Err(_) => None,
+        Ok(path) => {
+            if !path.is_empty() {
+                Some(vec![path])
+            } else {
+                panic!("Missing LVM_HOME environment variable");
+            }
+        }
+        Err(_) => panic!("Failure to get environments"),
     };
+
     // Tell Cargo that if the given file changes, to rerun this build script.
     println!("cargo:rerun-if-changed=src/flutter_ffi.rs");
     // settings for fbr_codegen