Fix zero_ptr suggestion for no_std crates

Author: Jarcho

tests/ui/zero_ptr_no_std.fixed

@@ -0,0 +1,21 @@
+// run-rustfix
+
+#![feature(lang_items, start, libc)]
+#![no_std]
+#![deny(clippy::zero_ptr)]
+
+#[start]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    let _ = core::ptr::null::<usize>();
+    let _ = core::ptr::null_mut::<f64>();
+    let _: *const u8 = core::ptr::null();
+    0
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}

tests/ui/zero_ptr_no_std.rs

@@ -0,0 +1,21 @@
+// run-rustfix
+
+#![feature(lang_items, start, libc)]
+#![no_std]
+#![deny(clippy::zero_ptr)]
+
+#[start]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    let _ = 0 as *const usize;
+    let _ = 0 as *mut f64;
+    let _: *const u8 = 0 as *const _;
+    0
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}

tests/ui/zero_ptr_no_std.stderr

@@ -0,0 +1,26 @@
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr_no_std.rs:9:13
+   |
+LL |     let _ = 0 as *const usize;
+   |             ^^^^^^^^^^^^^^^^^ help: try: `core::ptr::null::<usize>()`
+   |
+note: the lint level is defined here
+  --> $DIR/zero_ptr_no_std.rs:5:9
+   |
+LL | #![deny(clippy::zero_ptr)]
+   |         ^^^^^^^^^^^^^^^^
+
+error: `0 as *mut _` detected
+  --> $DIR/zero_ptr_no_std.rs:10:13
+   |
+LL |     let _ = 0 as *mut f64;
+   |             ^^^^^^^^^^^^^ help: try: `core::ptr::null_mut::<f64>()`
+
+error: `0 as *const _` detected
+  --> $DIR/zero_ptr_no_std.rs:11:24
+   |
+LL |     let _: *const u8 = 0 as *const _;
+   |                        ^^^^^^^^^^^^^ help: try: `core::ptr::null()`
+
+error: aborting due to 3 previous errors
+