making wireguard work on RHEL7/etc.

[wireguard at wut.to]

Jason A. Donenfeld wrote:

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

A quick look around found this, I think conditional code on RHEL_MAJOR is
probably the way to go, maybe "If KERNEL_VERSION() or RHEL_MAJOR then
<compat blah>"

$ cat /usr/include/linux/version.h

#define LINUX_VERSION_CODE 199168
#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))
#define RHEL_MAJOR 7
#define RHEL_MINOR 3
#define RHEL_RELEASE_VERSION(a,b) (((a) << 8) + (b))
#define RHEL_RELEASE_CODE 1795
#define RHEL_RELEASE "514.21.2"