I ran into this issue after doing a manual react-native link
of a dependency which didn't support auto link on RN 0.59+
The solution was to select the xcodeproj file under the Libraries folder in Xcode and then in Build Settings, change Header Search Paths to add these two (recursive):
$(SRCROOT)/../../../ios/Pods/Headers/Public/React-Core
$(SRCROOT)/../../../ios/Pods/Headers/Public