[cxx-interop] Cast data to the correct type.

The implicit conversions are OK in C but C++ will error. To make this
header valid in both C and C++ we should just always cast.

Author: zoecarver

stdlib/public/SwiftShims/DispatchOverlayShims.h

@@ -215,8 +215,8 @@ static inline unsigned int
 _swift_dispatch_data_apply(
     __swift_shims_dispatch_data_t data,
     __swift_shims_dispatch_data_applier SWIFT_DISPATCH_NOESCAPE applier) {
-  return dispatch_data_apply(data, ^bool(dispatch_data_t data, size_t off, const void *loc, size_t size){
-    return applier(data, off, loc, size);
+  return dispatch_data_apply((dispatch_data_t)data, ^bool(dispatch_data_t data, size_t off, const void *loc, size_t size){
+    return applier((__swift_shims_dispatch_data_t)data, off, loc, size);
   });
 }