Ignore empty RUSTC_WRAPPER in bootstrap

This change ignores the RUSTC_WRAPPER_REAL environment variable if it's set to the empty string. This matches cargo behaviour and allows users to easily shadow a globally set RUSTC_WRAPPER (which they might have set for non-rustc projects).

Author: Skepfyr

src/bootstrap/src/bin/rustc.rs

@@ -91,12 +91,13 @@ fn main() {
  rustc_real
  };
 
- let mut cmd = if let Some(wrapper) = env::var_os("RUSTC_WRAPPER_REAL") {
- let mut cmd = Command::new(wrapper);
- cmd.arg(rustc_driver);
- cmd
- } else {
- Command::new(rustc_driver)
+ let mut cmd = match env::var_os("RUSTC_WRAPPER_REAL") {
+ Some(wrapper) if !wrapper.is_empty() => {
+ let mut cmd = Command::new(wrapper);
+ cmd.arg(rustc_driver);
+ cmd
+ }
+ _ => Command::new(rustc_driver),
  };
  cmd.args(&args).env(dylib_path_var(), env::join_paths(&dylib_path).unwrap());