Add regression test for recursive type bug found a while ago when compiling Rust for Linux

tests/compile/recursive_types.rs

@@ -0,0 +1,22 @@
+// Compiler:
+
+// `Set` reaches itself by value through `*mut Root`, so a backend that emits `Root`'s
+// fields with the still-incomplete `Set` type fails to compile this.
+
+#![crate_type = "lib"]
+
+#[repr(C)]
+pub struct Set {
+    pub root: *mut Root,
+    pub first: usize,
+    pub second: usize,
+}
+
+#[repr(C)]
+pub struct Root {
+    pub default_set: Set,
+}
+
+pub fn identity(set: Set) -> Set {
+    set
+}