compiletest/rmake: avoid double test directory for rmake.rs tests

This is important for other tests that have various things like modes,
revisions and the like. These features are not supported in run-make
tests, so we don't need the double layering.

src/tools/compiletest/src/common.rs

@@ -760,8 +760,14 @@ pub fn output_testname_unique(
 /// test/revision should reside. Example:
 ///   /path/to/build/host-triple/test/ui/relative/testname.revision.mode/
 pub fn output_base_dir(config: &Config, testpaths: &TestPaths, revision: Option<&str>) -> PathBuf {
-    output_relative_path(config, &testpaths.relative_dir)
-        .join(output_testname_unique(config, testpaths, revision))
+    // In run-make tests, constructing a relative path + unique testname causes a double layering
+    // since revisions are not supported, causing unnecessary nesting.
+    if config.mode == Mode::RunMake {
+        output_relative_path(config, &testpaths.relative_dir)
+    } else {
+        output_relative_path(config, &testpaths.relative_dir)
+            .join(output_testname_unique(config, testpaths, revision))
+    }
 }
 
 /// Absolute path to the base filename used as output for the given