macos 26: Compiling now reqiures `xcrun cargo build`

[jschwe]

When compiling on macos 26, I now need to use xcrun cargo build for the build from source to succeed.
Probably we need to set some environment variable in our build-script to avoid that.

[jschwe]

Using xcrun printenv, it seems that setting SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk is sufficient to make cargo build work again.
Perhaps we could also wrap the native building in xcrun (when not cross-compiling) on macos?