force single-threaded text execution

src/test/rustdoc-ui/cfg-test.rs

@@ -1,5 +1,5 @@
 // build-pass (FIXME(62277): could be check-pass?)
-// compile-flags:--test
+// compile-flags:--test --test-args --test-threads=1
 // normalize-stdout-test: "src/test/rustdoc-ui" -> "$$DIR"
 
 // Crates like core have doctests gated on `cfg(not(test))` so we need to make

src/test/rustdoc-ui/cfg-test.stdout

@@ -1,7 +1,7 @@
 
 running 2 tests
-test $DIR/cfg-test.rs - Foo (line 20) ... ok
 test $DIR/cfg-test.rs - Bar (line 28) ... ok
+test $DIR/cfg-test.rs - Foo (line 20) ... ok
 
 test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out