add test for symbol mangling issue

tests/ui/eii/same-symbol.rs

@@ -0,0 +1,29 @@
+//@ run-pass
+//@ check-run-results
+//@ ignore-backends: gcc
+#![feature(extern_item_impls)]
+
+pub mod a {
+    #[eii(foo)]
+    pub fn foo();
+}
+
+pub mod b {
+    #[eii(foo)]
+    pub fn foo();
+}
+
+#[a::foo]
+fn a_foo_impl() {
+    println!("foo1");
+}
+
+#[b::foo]
+fn b_foo_impl() {
+    println!("foo2");
+}
+
+fn main() {
+    a::foo();
+    b::foo();
+}

tests/ui/eii/same-symbol.run.stdout

@@ -0,0 +1,2 @@
+foo1
+foo1