Hi Richard,
You should be able to target 5.4 out of the box with Xcode 16.2 (it can be downloaded on the Apple Developer site Unauthorized - Apple Developer). 16.3 unfortunately includes a major versoin update to Clang (16 to 17) which adds a lot of new warnings and various other issues. I’ll point you to a mainline CL that brings 16.3 compliance once it goes though on our end.
Best regards.