Auto merge of #43109 - pnkfelix:fix-link_args-gate, r=nikomatsakis

Fix feature gate for `#[link_args(..)]` attribute

Fix feature gate for `#[link_args(..)]` attribute so that it will fire regardless of context of attribute.

See also #29596 and #43106

src/test/compile-fail/gated-link-args.rs

@@ -9,12 +9,22 @@
 // except according to those terms.
 
 // Test that `#[link_args]` attribute is gated by `link_args`
-// feature gate.
+// feature gate, both when it occurs where expected (atop
+// `extern { }` blocks) and where unexpected.
 
 // gate-test-link_args
 
-#[link_args = "aFdEfSeVEEE"]
-extern {}
-//~^ ERROR the `link_args` attribute is not portable across platforms
+// sidestep warning (which is correct, but misleading for
+// purposes of this test)
+#![allow(unused_attributes)]
 
-fn main() { }
+#![link_args = "-l unexpected_use_as_inner_attr_on_mod"]
+//~^ ERROR the `link_args` attribute is experimental
+
+#[link_args = "-l expected_use_case"]
+//~^ ERROR the `link_args` attribute is experimental
+extern {}
+
+#[link_args = "-l unexected_use_on_non_extern_item"]
+//~^ ERROR: the `link_args` attribute is experimental
+fn main() {}