miri: accept extern types in structs if they are the only field

src/test/ui/consts/const-eval/issue-55541.rs

@@ -0,0 +1,21 @@
+// compile-pass
+
+// Test that we can handle newtypes wrapping extern types
+
+#![feature(extern_types, const_transmute)]
+
+extern "C" {
+  pub type ExternType;
+}
+unsafe impl Sync for ExternType {}
+
+#[repr(transparent)]
+pub struct Wrapper(ExternType);
+
+static MAGIC_FFI_STATIC: u8 = 42;
+
+pub static MAGIC_FFI_REF: &'static Wrapper = unsafe {
+  std::mem::transmute(&MAGIC_FFI_STATIC)
+};
+
+fn main() {}