[PATCH] compat: allow override of depmod basedir

[Jason A. Donenfeld]

Thanks for figuring this out. It looks like '/' as the default is
indeed safe, as this value is only used in this expression:

       cfg.dirnamelen = snprintf(cfg.dirname, PATH_MAX,
                                 "%s/lib/modules/%s",
                                 root == NULL ? "" : root, cfg.kversion);

and // and / are equivalent.

I've applied this with slight modifications here:
https://git.zx2c4.com/wireguard-linux-compat/commit/?id=6028795b4415d7f467acc01c5292f8e4703a6b39


Jason