gccrs: testsuite: Add empty string macro test

Add two new tests with empty string for include_str and include_bytes
macros.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1830_bytes.rs: New test.
	* rust/compile/issue-1830_str.rs: New test.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

gcc/testsuite/rust/compile/issue-1830_bytes.rs

@@ -0,0 +1,8 @@
+#[rustc_builtin_macro]
+macro_rules! include_bytes {
+    () => {{}};
+}
+
+fn main() {
+    include_bytes!(""); // { dg-excess-errors "Is a directory" }
+}

gcc/testsuite/rust/compile/issue-1830_str.rs

@@ -0,0 +1,8 @@
+#[rustc_builtin_macro]
+macro_rules! include_str {
+    () => {{}};
+}
+
+fn main() {
+    include_str!(""); // { dg-excess-errors "Is a directory" }
+}