fix compile-fail tests to avoid libstd debug assertions

tests/compile-fail/copy_null.rs

@@ -1,8 +1,14 @@
 //error-pattern: invalid use of NULL pointer
+#![feature(intrinsics)]
+
+// Directly call intrinsic to avoid debug assertions in libstd
+extern "rust-intrinsic" {
+    fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+}
 
 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); }
+    unsafe { copy_nonoverlapping(std::ptr::null(), ptr, 0); }
 }

tests/compile-fail/copy_overlapping.rs

@@ -1,12 +1,16 @@
-#![feature(core_intrinsics)]
-
 //error-pattern: copy_nonoverlapping called on overlapping ranges
+#![feature(intrinsics)]
+
+// Directly call intrinsic to avoid debug assertions in libstd
+extern "rust-intrinsic" {
+    fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+}
 
 fn main() {
     let mut data = [0u8; 16];
     unsafe {
         let a = data.as_mut_ptr();
         let b = a.wrapping_offset(1) as *mut _;
-        std::ptr::copy_nonoverlapping(a, b, 2);
+        copy_nonoverlapping(a, b, 2);
     }
 }

tests/compile-fail/copy_unaligned.rs

@@ -1,8 +1,14 @@
 //error-pattern: tried to access memory with alignment 1, but alignment 2 is required
+#![feature(intrinsics)]
+
+// Directly call intrinsic to avoid debug assertions in libstd
+extern "rust-intrinsic" {
+    fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
+}
 
 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); }
+    unsafe { copy_nonoverlapping(&data[5], ptr, 0); }
 }