
Commit 0abf6f830cd390e2e5dbd4a2c68f611f5c9507dc removed _boot.py from the manifest for the GENERIC_512K board because the build does not include a filesystem. But the main code expects _boot.py to be there and prints an error if it's not. So add a custom _boot.py, which just sets the gc.threshold(). Signed-off-by: Damien George <damien@micropython.org>