Ensure the language data always fits the reserved space in the XFLASH.
The script *should* use the LANG_SIZE definition from "xflash_layout",
which can be obtained by preprocessing the source code.
At the moment though this step has been omitted since running
arduino-builder to preprocess the source requires extra flags passed by
build.sh. The size has been hard-coded (and it's unlikely to change
given the content size is constant for the architecture).
