Migrate run-make/rustdoc-shared-flags to rmake

Author: GuillaumeGomez

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -253,7 +253,6 @@ run-make/rustdoc-scrape-examples-ordering/Makefile
 run-make/rustdoc-scrape-examples-remap/Makefile
 run-make/rustdoc-scrape-examples-test/Makefile
 run-make/rustdoc-scrape-examples-whitespace/Makefile
-run-make/rustdoc-shared-flags/Makefile
 run-make/rustdoc-target-spec-json-path/Makefile
 run-make/rustdoc-themes/Makefile
 run-make/rustdoc-verify-output-files/Makefile

tests/run-make/rustdoc-shared-flags/Makefile

@@ -0,0 +1,14 @@
+use run_make_support::{Diff, rustc, rustdoc};
+
+fn compare_outputs(args: &[&str]) {
+    let rustc_output = String::from_utf8(rustc().args(args).command_output().stdout).unwrap();
+    let rustdoc_output = String::from_utf8(rustdoc().args(args).command_output().stdout).unwrap();
+
+    Diff::new().expected_text("rustc", rustc_output).actual_text("rustdoc", rustdoc_output).run();
+}
+
+fn main() {
+    compare_outputs(&["-C", "help"]);
+    compare_outputs(&["-Z", "help"]);
+    compare_outputs(&["-C", "passes=list"]);
+}