Rollup merge of #145821 - lolbinarycat:compiletest-error-show, r=clubby789

compiletest: if a compiler fails, show its output

Before, when working on something like a `rustdoc-js` test, if you made a syntax error in a rust file, you would not get that error output unless you ran with `--verbose`, which would also cause an enormous amount of other output to be printed as well.  This can also lead to frustration in new contributors who don't think to run with `--verbose`.

Now, if rustc or rustdoc is run by compiletest and produces an non-zero exit code, its output will be printed.

src/tools/compiletest/src/runtest.rs

@@ -412,7 +412,7 @@ impl<'test> TestCx<'test> {
             cmdline: format!("{cmd:?}"),
         };
         self.dump_output(
-            self.config.verbose,
+            self.config.verbose || !proc_res.status.success(),
             &cmd.get_program().to_string_lossy(),
             &proc_res.stdout,
             &proc_res.stderr,
@@ -1486,7 +1486,7 @@ impl<'test> TestCx<'test> {
         };
 
         self.dump_output(
-            self.config.verbose,
+            self.config.verbose || (!result.status.success() && self.config.mode != TestMode::Ui),
             &command.get_program().to_string_lossy(),
             &result.stdout,
             &result.stderr,
@@ -2987,6 +2987,7 @@ struct ProcArgs {
     args: Vec<OsString>,
 }
 
+#[derive(Debug)]
 pub struct ProcRes {
     status: ExitStatus,
     stdout: String,