Rollup merge of #114139 - Urgau:make-print-with-path-unstable, r=jackh726

Make `--print` with path unstable

https://github.com/rust-lang/rust/pull/113780 should have gone through an MCP+FCP but wasn't, but instead of reverting the original PR, this PR just make that new option unstable.

[Zulip discussion](https://rust-lang.zulipchat.com/#narrow/stream/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202023-07-27/near/379199738)
cc `@dtolnay`

compiler/rustc_session/src/config.rs

@@ -2152,6 +2152,12 @@ fn collect_print_requests(
     prints.extend(matches.opt_strs("print").into_iter().map(|req| {
         let (req, out) = split_out_file_name(&req);
 
+        if out.is_some() && !unstable_opts.unstable_options {
+            handler.early_error(
+                "the `-Z unstable-options` flag must also be passed to \
+                 enable the path print option",
+            );
+        }
         let kind = match PRINT_KINDS.iter().find(|&&(name, _)| name == req) {
             Some((_, PrintKind::TargetSpec)) => {
                 if unstable_opts.unstable_options {