The MPLAB® C18 Compiler is no longer supported, Microchip provides the MPLAB® XC8 compiler instead. We have a "MPLAB C18 to XC8 C Compiler Migration Guide". Another useful document is the "MPLAB XC8 Compiler User's Guide".
XC8 does not use linker scripts, instead, it provides options to control the linking and placement of the code. The compiler will invoke the linker automatically; you don't need to worry about using/invoking the linker unless you have a specific need to do so. XC8 will automatically execute the linker with all the necessary arguments. You will have to translate the C18 Linker Script settings to the equivalent Linker options under XC8.
Using the linker directly is not simple, and should be attempted only by those with a sound knowledge of the compiler, and linking in general.
