FPC 3.0.4a installs successfully on a clean macOS 10.14 "Mojave" install with Xcode and the command line tools installs.
On a clean Mojave install, with XCode and command-line tools installed, FPC will refuse to install as it does not recognize the command-line tools.
Additionally, the file /usr/lib/crt1.10.5.o remains missing.You don't need this file with the default /etc/fpc.cfg file generated by the FPC 3.0.4a installer, so you don't need to make a symlink.