test that we cannot access unescaped static memory with a raw ptr

Author: RalfJung

tests/compile-fail/stacked_borrows/unescaped_static.rs

@@ -0,0 +1,7 @@
+static ARRAY: [u8; 2] = [0, 1];
+
+fn main() {
+    let ptr_to_first = &ARRAY[0] as *const u8;
+    // Illegally use this to access the 2nd element.
+    let _val = unsafe { *ptr_to_first.add(1) }; //~ ERROR borrow stack
+}