making wireguard work on RHEL7/etc.

[Jason A. Donenfeld]

Hey,

Thanks so much for doing the mind numbing work of trudging through all
those ifdefs. Maintaining compat.h is truly a horrifying experience,
and now somebody can commiserate with me :).

Obviously these patches aren't mergable as-is, but it functions as a
treasure map for how to actually go about it.

Are you aware of any RHEL-specific defines I might be able to use to
differentiate?

Regards,
Jason