[AutoDiff] Add SR-12526 negative test.

Add negative test for SR-12526: `@derivative` attribute cross-module
deserialization crash.

Author: dan-zheng

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/Inputs/a.swift

@@ -0,0 +1,7 @@
+public struct Struct {
+  public func method(_ x: Float) -> Float { x }
+
+  public static func +(_ lhs: Self, rhs: Self) -> Self {
+    lhs
+  }
+}

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/Inputs/b.swift

@@ -0,0 +1,21 @@
+import _Differentiation
+import a
+
+extension Struct: Differentiable {
+  public struct TangentVector: Differentiable & AdditiveArithmetic {}
+  public mutating func move(along _: TangentVector) {}
+
+  @usableFromInline
+  @derivative(of: method, wrt: x)
+  func vjpMethod(_ x: Float) -> (value: Float, pullback: (Float) -> Float) {
+    (x, { $0 })
+  }
+
+  @usableFromInline
+  @derivative(of: +)
+  static func vjpAdd(_ lhs: Self, rhs: Self) -> (
+    value: Self, pullback: (TangentVector) -> (TangentVector, TangentVector)
+  ) {
+    (lhs + rhs, { v in (v, v) })
+  }
+}

test/AutoDiff/Sema/DerivativeRegistrationCrossModule/main.swift

@@ -0,0 +1,14 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -primary-file %S/Inputs/a.swift -emit-module-path %t/a.swiftmodule
+// RUN: %target-swift-frontend -emit-module -primary-file %S/Inputs/b.swift -emit-module-path %t/b.swiftmodule -I %t
+// RUN: not --crash %target-swift-frontend-typecheck -verify -I %t %s
+
+// SR-12526: Fix cross-module deserialization crash involving `@derivative` attribute.
+
+import a
+import b
+
+func foo(_ s: Struct) {
+  _ = Struct()
+  _ = s.method(1)
+}