chore: derive more type classes for IR data structures (#7085)

src/Lean/Compiler/IR/Basic.lean

@@ -180,7 +180,7 @@ structure CtorInfo where
   size : Nat
   usize : Nat
   ssize : Nat
-  deriving Repr
+  deriving Inhabited, Repr
 
 def CtorInfo.beq : CtorInfo → CtorInfo → Bool
   | ⟨n₁, cidx₁, size₁, usize₁, ssize₁⟩, ⟨n₂, cidx₂, size₂, usize₂, ssize₂⟩ =>
@@ -223,6 +223,7 @@ inductive Expr where
   | lit (v : LitVal)
   /-- Return `1 : uint8` Iff `RC(x) > 1` -/
   | isShared (x : VarId)
+  deriving Inhabited
 
 @[export lean_ir_mk_ctor_expr]  def mkCtorExpr (n : Name) (cidx : Nat) (size : Nat) (usize : Nat) (ssize : Nat) (ys : Array Arg) : Expr :=
   Expr.ctor ⟨n, cidx, size, usize, ssize⟩ ys

src/Lean/Compiler/IR/CtorLayout.lean

@@ -15,6 +15,7 @@ inductive CtorFieldInfo where
   | object (i : Nat)
   | usize  (i : Nat)
   | scalar (sz : Nat) (offset : Nat) (type : IRType)
+  deriving Inhabited
 
 namespace CtorFieldInfo