How to fix all Ruby "Failed to build gem native extension" Errors in OS X
cp /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg ~/Desktop && open ~/Desktop/macOS_SDK_headers_for_macOS_10.14.pkg
Boom. Now start removing all those pesky overrides you set in
All credit goes to the amazing João Rocha da Silva. Be sure to check out his detailed write-up on why you need to do this. TLDR; Mac OS X 10.14 no longer places the include libraries in the standard
/usr/include directory and locked by SIP.