Xcode 27 is building swift-syntax 603.0.2 from source

### Description

It looks like there is no swift-syntax prebuilt for 603.0.2 with Xcode 27.

Just tried to open our project that uses prebuilts in Xcode 26.6 and I can see swift-syntax being built in Xcode's build timeline (and the build is also ~25s slower than in Xcode 26.6).

Tried resetting caches already, no difference. We're only using swift-syntax for macros.

Is this expected? Am I just too early after release, or do we need to update to newer swift-syntax for this to work?

### Steps to Reproduce

_No response_

Start by comparing the Xcode 26.6 and Xcode 27 build timelines for the project using swift-syntax prebuilts, focusing on why 603.0.2 is built from source. Confirm whether a prebuilt exists for Xcode 27 and whether updating swift-syntax changes the behavior; done means documenting the expected behavior and the required version or release.

Written by the indexing model from the issue text.