@andyj
There is a 32-to-64 cross-compiler extension (toolchain64.tcz). You'd use that for the modules, standard compiletc for the apps. The env vars to export for such a cross-module build have been posted in this forum; search for my posts with CROSS_COMPILE.
@awabimakoto
DEBUGFS is info leaks and bloat; putting a switch like that there is completely the wrong place for it. Complain to upstream that it should be in /sys.