Add more precondition check tests

Author: saethlin

tests/ui/precondition-checks/nonoverlapping-misaligned.rs

@@ -0,0 +1,14 @@
+//@ run-fail
+//@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
+//@ error-pattern: unsafe precondition(s) violated: ptr::copy_nonoverlapping
+//@ ignore-debug
+
+fn main() {
+    let src: [u16; 2] = [0, 0];
+    let mut dst: [u16; 2] = [0, 0];
+    let src = src.as_ptr();
+    let dst = dst.as_mut_ptr();
+    unsafe {
+        std::ptr::copy_nonoverlapping(src.byte_add(1), dst, 1);
+    }
+}

tests/ui/precondition-checks/nonoverlapping-null.rs

@@ -0,0 +1,8 @@
+//@ run-pass
+//@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
+
+fn main() {
+    unsafe {
+        std::ptr::copy_nonoverlapping(std::ptr::null::<u8>(), std::ptr::null_mut(), 0);
+    }
+}

tests/ui/precondition-checks/nonoverlapping-overlapping.rs

@@ -0,0 +1,12 @@
+//@ run-fail
+//@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
+//@ error-pattern: unsafe precondition(s) violated: ptr::copy_nonoverlapping
+//@ ignore-debug
+
+fn main() {
+    let mut buf: [u8; 3] = [0, 1, 2];
+    let ptr = buf.as_mut_ptr();
+    unsafe {
+        std::ptr::copy_nonoverlapping(ptr, ptr.add(1), 2);
+    }
+}