Change expected objcImpl private let optimization

Previous changes have made it so that `private let`s in an objcImpl extension are implicitly `@objc`, which changed downstream behavior in a SILOptimizer test. The new behavior is actually more correct, so codify this behavior change by modifying the test.

Author: beccadax

test/SILOptimizer/let_properties_opts_objc.swift

@@ -16,12 +16,12 @@ public func testObjcInterface(_ x: ObjcInterface) -> Int {
   return x.i
 }
 
-// Test optimization of a private constant. This constant must be declared in a separate type without other fields.
+// Test that private @objc constants aren't optimized, but instead continue to pass through ObjC message dispatch.
 @_objcImplementation extension ObjcInterfaceConstInit {
   private let constant: Int = 0
 
   // CHECK-LABEL: sil hidden @$sSo22ObjcInterfaceConstInitC4testE0E15PrivateConstantSiyF : $@convention(method) (@guaranteed ObjcInterfaceConstInit) -> Int {
-  // CHECK: ref_element_addr [immutable] %0 : $ObjcInterfaceConstInit, #ObjcInterfaceConstInit.constant
+  // CHECK: objc_method %0 : $ObjcInterfaceConstInit, #ObjcInterfaceConstInit.constant!getter.foreign
   // CHECK-LABEL: } // end sil function '$sSo22ObjcInterfaceConstInitC4testE0E15PrivateConstantSiyF'
   final func testPrivateConstant() -> Int {
     return constant