uefi: Use slice equality rather than memcmp

`compiler_builtins` shouldn't be called directly. Change the `PartialEq`
implementation for `DevicePathNode` to use slice equality instead, which
will call `memcmp`/`bcmp` via the intrinsic.

Author: tgross35

library/std/src/sys/pal/uefi/helpers.rs

@@ -444,17 +444,17 @@ impl<'a> DevicePathNode<'a> {
 
 impl<'a> PartialEq for DevicePathNode<'a> {
     fn eq(&self, other: &Self) -> bool {
-        let self_len = self.length();
-        let other_len = other.length();
-
-        self_len == other_len
-            && unsafe {
-                compiler_builtins::mem::memcmp(
-                    self.protocol.as_ptr().cast(),
-                    other.protocol.as_ptr().cast(),
-                    usize::from(self_len),
-                ) == 0
-            }
+        // Compare as a single buffer rather than by field since it optimizes better.
+        //
+        // SAFETY: `Protocol` is followed by a buffer of `length - sizeof::<Protocol>()`. `Protocol`
+        // has no padding so it is sound to interpret as a slice.
+        unsafe {
+            let s1 =
+                slice::from_raw_parts(self.protocol.as_ptr().cast::<u8>(), self.length().into());
+            let s2 =
+                slice::from_raw_parts(other.protocol.as_ptr().cast::<u8>(), other.length().into());
+            s1 == s2
+        }
     }
 }