I noticed an unrelated issue on some CI machines that forced me to reset their CocoaPods cache/state. Afterwards I started seeing this error when compiling glog:
error: unable to find sdk: 'iphoneos'
AI pointed me at the Nix environment messing with the Apple compiler environment (same issue that necessitates native/scripts/run-react-native.sh). I was able to solve it by setting $DEVELOPER_DIR correctly.