add testcase for more than 3 cfg names

tests/ui/check-cfg/cfg-value-for-cfg-name-duplicate.rs

@@ -0,0 +1,12 @@
+// #120427
+// This test checks we won't suggest more than 3 span suggestions for cfg names
+//
+// check-pass
+// compile-flags: -Z unstable-options
+// compile-flags: --check-cfg=cfg(foo,values("value")) --check-cfg=cfg(bar,values("value")) --check-cfg=cfg(bee,values("value")) --check-cfg=cfg(cow,values("value"))
+
+#[cfg(value)]
+//~^ WARNING unexpected `cfg` condition name: `value`
+fn x() {}
+
+fn main() {}

tests/ui/check-cfg/cfg-value-for-cfg-name-duplicate.stderr

@@ -0,0 +1,13 @@
+warning: unexpected `cfg` condition name: `value`
+  --> $DIR/cfg-value-for-cfg-name-duplicate.rs:8:7
+   |
+LL | #[cfg(value)]
+   |       ^^^^^
+   |
+   = help: expected names are: `bar`, `bee`, `cow`, `debug_assertions`, `doc`, `doctest`, `foo`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `unix`, `windows`
+   = help: to expect this configuration use `--check-cfg=cfg(value)`
+   = note: see <https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html> for more information about checking conditional configuration
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: 1 warning emitted
+