xcbuild: include version in sdk

Without this xcbuild can detect an incorrect version for store paths
that have a sequence of digits in their hash.

ld: malformed 32-bit x.y.z version number: 85294

/nix/store/yz966rdvw1blblvzs15pxpcd85294isw-MacOSX.platform/Developer/SDKs/MacOSX.sdk