Identified unsoundness in preprocessor + cleanup of find_include_file.
Identified unsoundness in preprocessor + cleanup of find_include_file.

The unsoundness remains unfixed (and already existed before the cleanup)
and is explained in the comments added in this commit.

willempx/verifast,willempx/verifast,willempx/verifast,willempx/verifast,willempx/verifast