Firebase Undefined symbols for architecture x86_64

Just discovered a similar problem and got it solved by clearing Pod-Cache.

Clear CocoaPods Cache

pod deintegrate && pod cache clean --all

Re-Install Pods

pod install

For me I just installed Firebase framework to Xcode, not using CocoaPods due to other unsolvable issues. After build there is similar errors like above with "symbol(s) not found for architecture x86_64". (maybe because I am working with Xcode on VMWare)

Then I have to manually go to General - Linked Frameworks and Libraries and add:

libsqlite3.tbd, libz.tbd, libc++.tbd

for the project to work.