private void checkCallFixup(DocInfo doc) throws SleighException {
		CompilerSpec cspec = program.getCompilerSpec();
		PcodeInjectLibrary injectLibrary = cspec.getPcodeInjectLibrary();
		InjectPayload payload =
			injectLibrary.getPayload(InjectPayload.CALLFIXUP_TYPE, doc.formalName);
		if (payload == null) {
			return;
		}
		if (injectLibrary.hasProgramPayload(doc.formalName, InjectPayload.CALLFIXUP_TYPE)) {
			return;
		}
		throw new SleighException("Extension cannot replace callfixup: " + doc.formalName);
	}
Check that the proposed callfixup extension does not collide with built-in fixups
@param doc is info about the proposed extension
@throws SleighException is there is a collision
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/SpecExtension.java