compiler: add Deref to AbiAlign to ease transition

We will want to remove many cases of `.abi`, including `.abi.thing`,
so this may simplify future PRs and certainly doesn't hurt.

We omit DerefMut because mutation is much rarer and localized.

compiler/rustc_abi/src/lib.rs

@@ -43,7 +43,7 @@
 #[cfg(feature = "nightly")]
 use std::iter::Step;
 use std::num::{NonZeroUsize, ParseIntError};
-use std::ops::{Add, AddAssign, Mul, RangeInclusive, Sub};
+use std::ops::{Add, AddAssign, Deref, Mul, RangeInclusive, Sub};
 use std::str::FromStr;
 
 use bitflags::bitflags;
@@ -884,6 +884,14 @@ pub fn max(self, other: AbiAlign) -> AbiAlign {
     }
 }
 
+impl Deref for AbiAlign {
+    type Target = Align;
+
+    fn deref(&self) -> &Self::Target {
+        &self.abi
+    }
+}
+
 /// Integers, also used for enum discriminants.
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 #[cfg_attr(