Add test case

Author: wesleywiser

src/test/codegen/auxiliary/static_dllimport_aux.rs

@@ -0,0 +1,13 @@
+use std::sync::atomic::{AtomicPtr, Ordering};
+
+#[inline(always)]
+pub fn memrchr() {
+    fn detect() {}
+
+    static CROSS_CRATE_STATIC_ITEM: AtomicPtr<()> = AtomicPtr::new(detect as *mut ());
+
+    unsafe {
+        let fun = CROSS_CRATE_STATIC_ITEM.load(Ordering::SeqCst);
+        std::mem::transmute::<*mut (), fn()>(fun)()
+    }
+}

src/test/codegen/issue-81408-dllimport-thinlto-windows.rs

@@ -0,0 +1,15 @@
+// compile-flags: -O -C lto=thin -C prefer-dynamic=no
+// only-windows
+// aux-build:static_dllimport_aux.rs
+
+// Test that on Windows, when performing ThinLTO, we do not mark cross-crate static items with
+// dllimport because lld does not fix the symbol names for us.
+
+extern crate static_dllimport_aux;
+
+// CHECK-LABEL: @{{.+}}CROSS_CRATE_STATIC_ITEM{{.+}} =
+// CHECK-SAME: external dllimport local_unnamed_addr global %"{{.+}}::AtomicPtr
+
+pub fn main() {
+    static_dllimport_aux::memrchr();
+}