Since I got myself an ARM Chromebook, I made it a goal to be able to work on X15 directly on that small device. This implies cross compiling from ARM (actually aarch64) to x86, and running it in an emulator.
I used Crosstool-NG to generate two toolchains, available at http://ftp.sceen.net/ctng/aarch64/, and had to build QEMU from recent sources to work around a bug in the stable Debian packages. The build system was slightly improved to make it as convenient as possible, by inferring the toolchain name from the CC variable alone. Running QEMU was integrated into the build system to automatically use the toolchain as needed.