resolve: Absolute paths may be undetermined on 2018 edition

due to macro-expanded `extern crate` items adding names to extern prelude.

Author: petrochenkov

src/librustc_resolve/resolve_imports.rs

@@ -226,6 +226,9 @@ impl<'a, 'crateloader> Resolver<'a, 'crateloader> {
                         let module = self.get_module(binding.def().def_id());
                         self.populate_module_if_necessary(module);
                         return Ok(binding);
+                    } else if !self.graph_root.unresolved_invocations.borrow().is_empty() {
+                        // Macro-expanded `extern crate`items still can add names to extern prelude.
+                        return Err(Undetermined);
                     } else {
                         return Err(Determined);
                     }

src/test/ui/imports/extern-prelude-extern-crate-absolute-expanded.rs

@@ -0,0 +1,18 @@
+// compile-pass
+// edition:2018
+
+#![feature(extern_crate_item_prelude)]
+
+macro_rules! define_iso { () => {
+    extern crate std as iso;
+}}
+
+::iso::thread_local! {
+    static S: u8 = 0;
+}
+
+define_iso!();
+
+fn main() {
+    let s = S;
+}