Windows: Test if \\.\NUL works as an input file

tests/run-make/dos-device-input/rmake.rs

@@ -0,0 +1,9 @@
+//@ only-windows
+// Reason: dos devices are a Windows thing
+
+use run_make_support::rustc;
+
+fn main() {
+    rustc().input(r"\\.\NUL").crate_type("staticlib").run();
+    rustc().input(r"\\?\NUL").crate_type("staticlib").run();
+}