rustc_{a,l,m,t}san: re-run build script if env var LLVM_CONFIG changes

src/librustc_asan/build.rs

@@ -32,4 +32,5 @@ fn main() {
             .build_target("asan")
             .build();
     }
+    println!("cargo:rerun-if-env-changed=LLVM_CONFIG");
 }

src/librustc_lsan/build.rs

@@ -32,4 +32,5 @@ fn main() {
             .build_target("lsan")
             .build();
     }
+    println!("cargo:rerun-if-env-changed=LLVM_CONFIG");
 }

src/librustc_msan/build.rs

@@ -32,4 +32,5 @@ fn main() {
             .build_target("msan")
             .build();
     }
+    println!("cargo:rerun-if-env-changed=LLVM_CONFIG");
 }

src/librustc_tsan/build.rs

@@ -32,4 +32,5 @@ fn main() {
             .build_target("tsan")
             .build();
     }
+    println!("cargo:rerun-if-env-changed=LLVM_CONFIG");
 }