If we are building for both macOS HOSTS, there's no need to check and print that the SDK exists two times.
Currently a Guix build for both HOSTS will print:
./contrib/guix/guix-build
Found macOS SDK at '/SDKs/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers', using...
Found macOS SDK at '/SDKs/Xcode-12.2-12B45b-extracted-SDK-with-libcxx-headers', using...
Checking that we can connect to the guix-daemon...