Rollup merge of #44138 - steveklabnik:rustdoc-deprecations, r=QuietMisdreavus

Deprecate several flags in rustdoc

Part of #44136

cc @rust-lang/dev-tools @rust-lang/docs

This is a very basic PR to start deprecating some flags; `rustdoc` doesn't really have fancy output options like `rustc` does, so I went with `eprintln!`. Happy to change it if people feel that's not appropriate.

Also, I have no idea if we can or should write tests here, so I didn't try. If someone feels strongly about it, then let's do it, but given that the only outcome here is a side effect...

src/test/rustdoc/empty-mod-private.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags: --no-defaults --passes collapse-docs --passes unindent-comments --passes strip-priv-imports
+// compile-flags: --document-private-items
 
 // @has 'empty_mod_private/index.html' '//a[@href="foo/index.html"]' 'foo'
 // @has 'empty_mod_private/sidebar-items.js' 'foo'

src/test/rustdoc/issue-15347.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags:--no-defaults --passes collapse-docs --passes unindent-comments
+// compile-flags: --no-defaults --passes collapse-docs --passes unindent-comments
 
 // @has issue_15347/fn.foo.html
 #[doc(hidden)]

src/test/rustdoc/pub-method.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 // ignore-tidy-linelength
-// compile-flags: --no-defaults --passes collapse-docs --passes unindent-comments --passes strip-priv-imports
+// compile-flags: --document-private-items
 
 #![crate_name = "foo"]