This will allow for other types of root filesystems that don't rely on Buildroot
to be added and used in the future.
Propagate --verbose on all build scripts to see full GCC commands.
build-all: allow for neat subsets
also 9p share rootfs_overlay. TODO document.
Notice that Python sucks and does SIGPIPE annoyances, for now work around
by grepping the output file...
Fix the exit status read check with 'b', it broke down occasionally with:
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 1832: invalid start byte
