Running into the same issue here after upgrading from 0.44. None of the above solutions or clearing caches did the trick for me. Here's what I did to get things working again:
In the Terminal, navigate to the react-native/third-party/glog folder inside node_modules (for me, this was cd node_modules/react-native/third-party/glog-0.3.4) Once actively in this folder, run ../../scripts/ios-configure-glog.sh Glog is configured and the required config.h header file is created for Xcode to find