gccrs: Add test case to show issue is fixed

Fixes #1048

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1048.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

Author: philberty

gcc/testsuite/rust/compile/issue-1048.rs

@@ -0,0 +1,8 @@
+macro_rules! maybe_return { ($e:expr) => ($e); }
+
+fn frob(x: i32) -> i32{
+    maybe_return! {x}
+    // { dg-error "mismatched types. expected .... but got .i32. .E0308." "" { target *-*-* } .-1 }
+    // should return -1 
+    -1
+}