Work around RA's RUSTC_WRAPPER poisoning all subsequent command-line …

…builds

build.rs

@@ -65,6 +65,8 @@ fn main() {
 }
 
 fn compile_probe() -> Option<ExitStatus> {
+    println!("cargo:rerun-if-env-changed=RUSTC_WRAPPER");
+
     let rustc = env::var_os("RUSTC")?;
     let out_dir = env::var_os("OUT_DIR")?;
     let probefile = Path::new(&out_dir).join("probe.rs");