Rollup merge of #97411 - raiyansayeed:print-stderr-consistently, r=Mark-Simulacrum

Print stderr consistently

Solves https://github.com/rust-lang/rust/issues/96712

I tried to follow what I perceived as the general consensus for error messages in boostrap i.e messages that were ..
* resulting from an Err(...) =>
* literally called as "Error: ...."
* by the end of the block scope forced to run a panic! or process::exit with a guaranteed non-zero error code.

src/bootstrap/lib.rs

@@ -689,9 +689,9 @@ impl Build {
         // Check for postponed failures from `test --no-fail-fast`.
         let failures = self.delayed_failures.borrow();
         if failures.len() > 0 {
-            println!("\n{} command(s) did not execute successfully:\n", failures.len());
+            eprintln!("\n{} command(s) did not execute successfully:\n", failures.len());
             for failure in failures.iter() {
-                println!("  - {}\n", failure);
+                eprintln!("  - {}\n", failure);
             }
             process::exit(1);
         }