Yes, casey is right. Short (but not quick) way is:
download current stage3 from https://www.gentoo.org/downloads/ - use correct stage3 for your architecture
unzip/untar it to /:
xz --decompress stage3-*.xz
tar -xvf stage3*.tar -C /
emerge all again (this will take a lot of time)
emerge -avqeDN @world
For those running into the same issue on Windows under MSYS2 (using the GCC Suite to compile a shared library, linking an executable to that library, and then finding that dependencies are missing at runtime) you can,
copy the shared library to the same directory as the executable.
link to the shared library from the same directory as the executable.
The ldd command tries to link an executable or library to shared libraries in your system just as it happens when you run / use it. It will read library references from the given file and try to find them in your file system and path (LD_LIBRARY_PATH). If it displays "???" then this means that it cannot find some libraries in your system (and the program / ...
ppp-2.4.1 sources can be downloaded here: https://download.samba.org/pub/ppp/
the build instructions are classic: first you configure the build by running the configure script at the top of the source directory.
If the configuration does not work, it can be helpful to know that the preprocessor is responsible for finding includes.