Add test for merged features

Author: GuillaumeGomez

src/test/ui/rustdoc/renamed-features-rustdoc_internals.rs

@@ -0,0 +1,5 @@
+#![feature(doc_keyword)] //~ ERROR
+#![feature(doc_primitive)] //~ ERROR
+#![crate_type = "lib"]
+
+pub fn foo() {}

src/test/ui/rustdoc/renamed-features-rustdoc_internals.stderr

@@ -0,0 +1,19 @@
+error[E0557]: feature has been removed
+  --> $DIR/renamed-features-rustdoc_internals.rs:1:12
+   |
+LL | #![feature(doc_keyword)]
+   |            ^^^^^^^^^^^ feature has been removed
+   |
+   = note: merged into `#![feature(rustdoc_internals)]`
+
+error[E0557]: feature has been removed
+  --> $DIR/renamed-features-rustdoc_internals.rs:2:12
+   |
+LL | #![feature(doc_primitive)]
+   |            ^^^^^^^^^^^^^ feature has been removed
+   |
+   = note: merged into `#![feature(rustdoc_internals)]`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0557`.