Hi!
iASL lacks compatibility with older ACPI-drivers after some version (somewhere in early 2016). As a result, coreboot DSDT wasn't accepted by early 2.6 versions of Linux (and in all 2.4). iASL from coreboot 4.3 is OK, but iASL from coreboot 4.4 already generates incompatibility AML-bytecode.
Maybe you have the same problem, and Windows XP ACPI-driver (did you sure, that Windows XP bound to version 1.x? Not 2.x?) just didn't understand output of modern iASL?