resolve: Fix doc links referring to other crates when documenting proc macro crates directly

tests/rustdoc-ui/intra-doc/proc-macro-doc.rs

@@ -0,0 +1,27 @@
+// check-pass
+// force-host
+// no-prefer-dynamic
+// compile-flags: --crate-type proc-macro
+
+#![deny(rustdoc::broken_intra_doc_links)]
+
+extern crate proc_macro;
+use proc_macro::*;
+
+/// [`Unpin`]
+#[proc_macro_derive(F)]
+pub fn derive_(t: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    t
+}
+
+/// [`Vec`]
+#[proc_macro_attribute]
+pub fn attr(t: proc_macro::TokenStream, _: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    t
+}
+
+/// [`std::fs::File`]
+#[proc_macro]
+pub fn func(t: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    t
+}