symbol(s) not found for architecture x86_64

react native ^0.59.10.
react: 16.8.3
react-native-fcm 16.2.4

Undefined symbols for architecture x86_64:
"_FIRMessagingConnectionStateChangedNotification", referenced from:
-[RNFIRMessaging init] in libRNFIRMessaging.a(RNFIRMessaging.o)
"_FIRMessagingSendErrorNotification", referenced from:
-[RNFIRMessaging init] in libRNFIRMessaging.a(RNFIRMessaging.o)
"_FIRMessagingSendSuccessNotification", referenced from:
-[RNFIRMessaging init] in libRNFIRMessaging.a(RNFIRMessaging.o)
"_OBJC_CLASS_$_FIRApp", referenced from:
objc-class-ref in AppDelegate.o
"_OBJC_CLASS_$_FIRInstanceID", referenced from:
objc-class-ref in libRNFIRMessaging.a(RNFIRMessaging.o)
"_OBJC_CLASS_$_FIRMessaging", referenced from:
objc-class-ref in libRNFIRMessaging.a(RNFIRMessaging.o)
"_OBJC_CLASS_$_FIROptions", referenced from:
objc-class-ref in libRNFIRMessaging.a(RNFIRMessaging.o)
"_kFIRInstanceIDScopeFirebaseMessaging", referenced from:
-[RNFIRMessaging getEntityFCMToken:rejecter:] in libRNFIRMessaging.a(RNFIRMessaging.o)
-[RNFIRMessaging deleteEntityFCMToken:rejecter:] in libRNFIRMessaging.a(RNFIRMessaging.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Start by reproducing the iOS x86_64 link failure with React Native 0.59.10, react-native-fcm 16.2.4, and the Firebase versions used by the app. Inspect the references from AppDelegate.o and libRNFIRMessaging.a, then consider the issue done when the listed Firebase symbols link successfully in an iOS build.

Written by the indexing model from the issue text.