Auto merge of #14153 - Urgau:builtin_cfgs_lint, r=ehuss

Allow `unexpected_builtin_cfgs` lint in `user_specific_cfgs` test

### What does this PR try to resolve?

This PR allows the to be added `unexpected_builtin_cfgs` lint from rust-lang/rust#126158 in the `user_specific_cfgs_are_filtered_out` test in order to be able to merge the lint in rust-lang/rust CI.

### How should we test and review this PR?

The new lint is described in rust-lang/rust#126158 (comment) and testing should be "as simple" as executing the test with my rustc branch.

### Additional information

rust-lang/rust#126158 (comment) shows the test failing with the addition of the lint.

tests/testsuite/build.rs

@@ -6575,7 +6575,7 @@ fn user_specific_cfgs_are_filtered_out() {
         )
         .build();
 
-    p.cargo("rustc -- --cfg debug_assertions --cfg proc_macro")
+    p.cargo("rustc -- --cfg debug_assertions --cfg proc_macro -Aunknown_lints -Aunexpected_builtin_cfgs")
         .run();
     p.process(&p.bin("foo")).run();
 }