add some compile-fail tests

tests/compile-fail/copy_null.rs

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+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//error-pattern: invalid use of NULL pointer
+
+fn main() {
+    let mut data = [0u16; 4];
+    let ptr = &mut data[0] as *mut u16;
+    // Even copying 0 elements from NULL should error
+    unsafe { ptr.copy_from(std::ptr::null(), 0); }
+}

tests/compile-fail/copy_unaligned.rs

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+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//error-pattern: tried to access memory with alignment 1, but alignment 2 is required
+
+fn main() {
+    let mut data = [0u16; 8];
+    let ptr = (&mut data[0] as *mut u16 as *mut u8).wrapping_add(1) as *mut u16;
+    // Even copying 0 elements to something unaligned should error
+    unsafe { ptr.copy_from(&data[5], 0); }
+}