@Override
	public boolean extractAddend() {
		return !relocationTable.hasAddendRelocations() && !useSavedAddend;
	}
Get the preferred GP.
NOTE: This needs work to properly handle the use of multiple GP's
@return preferred GP value or -1 if unable to determine GP
Ghidra/Processors/MIPS/src/main/java/ghidra/app/util/bin/format/elf/relocation/MIPS_ElfRelocationContext.java