The first set of variables controls the directories that are recognized in the makefile. They should not be set in the Makefile.fpc file, but can be specified on the command line.
This is a list of directories, separated by spaces, that will be added as include directories to the compiler command line. Each directory in the list is prepended with -Fi and added to the compiler options.
This is a list of directories, separated by spaces, that will be added as unit search directories to the compiler command line. Each directory in the list is prepended with -Fu and added to the compiler options.
Is a list of library paths, separated by spaces. Each directory in the list is prepended with -Fl and added to the compiler options.
Is a list of object file directories, separated by spaces, that is added to the object files path, i.e. Each directory in the list is prepended with -Fo.