make another test more robust against random alignment

tests/compile-fail/unaligned_pointers/unaligned_ptr_addr_of.rs

@@ -4,9 +4,11 @@
 use std::ptr;
 
 fn main() {
-    let x = [2u16, 3, 4]; // Make it big enough so we don't get an out-of-bounds error.
-    let x = &x[0] as *const _ as *const u32;
-    // This must fail because alignment is violated: the allocation's base is not sufficiently aligned.
-    // The deref is UB even if we just put the result into a raw pointer.
-    let _x = unsafe { ptr::raw_const!(*x) }; //~ ERROR memory with alignment 2, but alignment 4 is required
+    for _ in 0..10 { // Try many times as this might work by chance.
+        let x = [2u16, 3, 4]; // Make it big enough so we don't get an out-of-bounds error.
+        let x = &x[0] as *const _ as *const u32;
+        // This must fail because alignment is violated: the allocation's base is not sufficiently aligned.
+        // The deref is UB even if we just put the result into a raw pointer.
+        let _x = unsafe { ptr::raw_const!(*x) }; //~ ERROR memory with alignment 2, but alignment 4 is required
+    }
 }