It really doesn't take long to change the code to XC8. You will have mega issues to get any peripheral libraries working, The latest C18 was 3.47 but you can't get it without pleading with Microchip.
The /p option is set in the build options ( but normally automatic ) You may need to go back to MPLAB v8.xx to compile this. That version( thankfully) is in the archive.
Its the linker whinging, not the compiler.. Also, be aware that the eval version is very bloated and may, depending on the amount of code, not fit.
Your best bet is to get the old peripheral libraries and run it in the much newer XC8. It should compile off the bat.