add ptr_offset_from OOB test, and update test errors

tests/compile-fail/intrinsics/copy_null.rs

@@ -9,5 +9,5 @@ fn main() {
     let mut data = [0u16; 4];
     let ptr = &mut data[0] as *mut u16;
     // Even copying 0 elements from NULL should error.
-    unsafe { copy_nonoverlapping(std::ptr::null(), ptr, 0); } //~ ERROR: memory access failed: 0x0 is not a valid pointer
+    unsafe { copy_nonoverlapping(std::ptr::null(), ptr, 0); } //~ ERROR: memory access failed: null pointer is not a valid pointer
 }

tests/compile-fail/intrinsics/ptr_offset_0_plus_0.rs

@@ -1,4 +1,4 @@
-// error-pattern: pointer arithmetic failed: 0x0 is not a valid pointer
+// error-pattern: pointer arithmetic failed: null pointer is not a valid pointer
 
 fn main() {
     let x = 0 as *mut i32;

tests/compile-fail/intrinsics/ptr_offset_from_oob.rs

@@ -0,0 +1,11 @@
+#![feature(core_intrinsics)]
+
+use std::intrinsics::ptr_offset_from;
+
+fn main() {
+    let start_ptr = &4 as *const _ as *const u8;
+    let length = 10;
+    let end_ptr = start_ptr.wrapping_add(length);
+    // Even if the offset is 0, a dangling OOB pointer is not allowed.
+    unsafe { ptr_offset_from(end_ptr, end_ptr) }; //~ERROR pointer at offset 10 is out-of-bounds
+}

tests/compile-fail/intrinsics/write_bytes_null.rs

@@ -6,5 +6,5 @@ extern "rust-intrinsic" {
 }
 
 fn main() {
-    unsafe { write_bytes::<u8>(std::ptr::null_mut(), 0, 0) }; //~ ERROR memory access failed: 0x0 is not a valid pointer
+    unsafe { write_bytes::<u8>(std::ptr::null_mut(), 0, 0) }; //~ ERROR memory access failed: null pointer is not a valid pointer
 }

tests/compile-fail/null_pointer_deref_zst.rs

@@ -3,6 +3,6 @@
 
 #[allow(deref_nullptr)]
 fn main() {
-    let x: () = unsafe { *std::ptr::null() }; //~ ERROR dereferencing pointer failed: 0x0 is not a valid pointer
+    let x: () = unsafe { *std::ptr::null() }; //~ ERROR dereferencing pointer failed: null pointer is not a valid pointer
     panic!("this should never print: {:?}", x);
 }

tests/compile-fail/null_pointer_write_zst.rs

@@ -1,6 +1,6 @@
 // Some optimizations remove ZST accesses, thus masking this UB.
 // compile-flags: -Zmir-opt-level=0
-// error-pattern: memory access failed: 0x0 is not a valid pointer
+// error-pattern: memory access failed: null pointer is not a valid pointer
 
 #[allow(deref_nullptr)]
 fn main() {