Delete executables if the test ran successfully.

This isn't a perfect heuristic, but since the amount of run-fail tests
is far lower than run-pass tests for now, it should be sufficient to
ensure that we don't run into CI limits. This makes it possible to run
the test binary manually (e.g., under gdb/lldb) if it failed to attempt
to find out why.

src/tools/compiletest/src/runtest.rs

@@ -1400,9 +1400,11 @@ impl<'test> TestCx<'test> {
             }
         };
 
-        // delete the executable after running it to save space.
-        // it is ok if the deletion failed.
-        let _ = fs::remove_file(self.make_exe_name());
+        if proc_res.status.success() {
+            // delete the executable after running it to save space.
+            // it is ok if the deletion failed.
+            let _ = fs::remove_file(self.make_exe_name());
+        }
 
         proc_res
     }