Rollup merge of #131053 - Urgau:print-check-cfg-doc, r=jieyouxu

Improve `--print=check-cfg` documentation
This PR improves the `--print=check-cfg` documentation by:
1. switching to a table for better readability
2. adding a clear indication where the specific check-cfg syntax starts
3. adding a link to the main `--check-cfg` documentation
`@rustbot` label +F-check-cfg

Author: matthiaskrgr

src/doc/unstable-book/src/compiler-flags/print-check-cfg.md

@@ -4,23 +4,28 @@ The tracking issue for this feature is: [#125704](https://github.com/rust-lang/r
 
 ------------------------
 
-This option of the `--print` flag print the list of expected cfgs.
+This option of the `--print` flag print the list of all the expected cfgs.
 
-This is related to the `--check-cfg` flag which allows specifying arbitrary expected
+This is related to the [`--check-cfg` flag][check-cfg] which allows specifying arbitrary expected
 names and values.
 
-This print option works similarly to `--print=cfg` (modulo check-cfg specifics):
--*check_cfg syntax*: *output of --print=check-cfg*
--`cfg(windows)`: `windows`
--`cfg(feature, values("foo", "bar"))`: `feature="foo"` and `feature="bar"`
--`cfg(feature, values(none(), ""))`: `feature` and `feature=""`
--`cfg(feature, values(any()))`: `feature=any()`
--`cfg(feature, values())`: `feature=`
--`cfg(any())`: `any()`
--*nothing*: `any()=any()`
+This print option works similarly to `--print=cfg` (modulo check-cfg specifics).
+
+|`--check-cfg`|`--print=check-cfg`|
+|-----------------------------------|-----------------------------|
+|`cfg(foo)`|`foo`|
+|`cfg(foo, values("bar"))`|`foo="bar"`|
+|`cfg(foo, values(none(), "bar"))`|`foo` & `foo="bar"`|
+||*check-cfg specific syntax*|
+|`cfg(foo, values(any())`|`foo=any()`|
+|`cfg(foo, values())`|`foo=`|
+|`cfg(any())`|`any()`|
+|*none*|`any()=any()`|
 
 To be used like this:
 
 ```bash
 rustc --print=check-cfg -Zunstable-options lib.rs
 ```
+
+[check-cfg]: https://doc.rust-lang.org/nightly/rustc/check-cfg.html