Add test for swap lint when no_std is present

Adds additional test to check for `swap` suggestion when `no_std` is present

Author: dswij

tests/ui/crate_level_checks/no_std_swap.rs

@@ -0,0 +1,15 @@
+#![no_std]
+#![feature(lang_items, start, libc)]
+#![crate_type = "lib"]
+
+use core::panic::PanicInfo;
+
+#[warn(clippy::all)]
+fn main() {
+    // TODO: do somethjing with swap
+    let mut a = 42;
+    let mut b = 1337;
+
+    a = b;
+    b = a;
+}

tests/ui/crate_level_checks/no_std_swap.stderr

@@ -0,0 +1,12 @@
+error: this looks like you are trying to swap `a` and `b`
+  --> $DIR/no_std_swap.rs:13:5
+   |
+LL | /     a = b;
+LL | |     b = a;
+   | |_________^ help: try: `core::mem::swap(&mut a, &mut b)`
+   |
+   = note: `-D clippy::almost-swapped` implied by `-D warnings`
+   = note: or maybe you should use `core::mem::replace`?
+
+error: aborting due to previous error
+