Rollup merge of #79058 - dtolnay:likelymacro, r=Mark-Simulacrum

Move likely/unlikely argument outside of invisible unsafe block

The previous `likely!`/`unlikely!` macros were unsound because it permits the caller's expr to contain arbitrary unsafe code.

```rust
pub fn huh() -> bool {
    likely!(std::ptr::read(&() as *const () as *const bool))
}
```

**Before:** compiles cleanly.
**After:**

```console
error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
   |
70 |     likely!(std::ptr::read(&() as *const () as *const bool))
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
   |
   = note: consult the function's documentation for information on how to avoid undefined behavior
```

compiler/rustc_data_structures/src/lib.rs

@@ -47,9 +47,9 @@ pub fn cold_path<F: FnOnce() -> R, R>(f: F) -> R {
 #[macro_export]
 macro_rules! likely {
     ($e:expr) => {
-        #[allow(unused_unsafe)]
-        {
-            unsafe { std::intrinsics::likely($e) }
+        match $e {
+            #[allow(unused_unsafe)]
+            e => unsafe { std::intrinsics::likely(e) },
         }
     };
 }
@@ -57,9 +57,9 @@ macro_rules! likely {
 #[macro_export]
 macro_rules! unlikely {
     ($e:expr) => {
-        #[allow(unused_unsafe)]
-        {
-            unsafe { std::intrinsics::unlikely($e) }
+        match $e {
+            #[allow(unused_unsafe)]
+            e => unsafe { std::intrinsics::unlikely(e) },
         }
     };
 }