Don't set test_harness to true by default as it would generate invalid code for combined doctests

Author: GuillaumeGomez

src/librustdoc/html/markdown.rs

@@ -894,7 +894,7 @@ impl LangString {
             no_run: false,
             ignore: Ignore::None,
             rust: true,
-            test_harness: true,
+            test_harness: false,
             compile_fail: false,
             error_codes: Vec::new(),
             edition: None,

tests/rustdoc-ui/doctest/cfg-test.stdout

@@ -1,7 +1,7 @@
 
 running 2 tests
-test $DIR/cfg-test.rs - Foo (line 19) ... ok
 test $DIR/cfg-test.rs - Bar (line 27) ... ok
+test $DIR/cfg-test.rs - Foo (line 19) ... ok
 
 test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 

tests/rustdoc-ui/doctest/doctest-output.stdout

@@ -1,8 +1,8 @@
 
 running 3 tests
 test $DIR/doctest-output.rs - (line 8) ... ok
-test $DIR/doctest-output.rs - foo::bar (line 18) ... ok
 test $DIR/doctest-output.rs - ExpandedStruct (line 24) ... ok
+test $DIR/doctest-output.rs - foo::bar (line 18) ... ok
 
 test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 

tests/rustdoc-ui/doctest/no-run-flag.stdout

@@ -1,7 +1,7 @@
 
 running 6 tests
-test $DIR/no-run-flag.rs - f (line 14) ... ignored
 test $DIR/no-run-flag.rs - f (line 11) ... ok
+test $DIR/no-run-flag.rs - f (line 14) ... ignored
 test $DIR/no-run-flag.rs - f (line 17) ... ok
 test $DIR/no-run-flag.rs - f (line 28) ... ok
 test $DIR/no-run-flag.rs - f (line 32) ... ok