strchrnul added in 15.4

[Ryan Carsten Schmidt]

On Apr 8, 2025, at 12:04, David Gilmanwrote:
> 
> If
> there are any ports, or the builders/the port system itself is
> definining MACOSX_DEPLOYMENT_TARGET to 15.0 they are at risk of
> tripping this when building on 15.4.

On macOS 15, MacPorts will set MACOSX_DEPLOYMENT_TARGET to 15.0. Similar for any other macOS version. (The minor macOS version is not included in the deployment target.)