mx4200.c Does Not Build on CentOS 7

My reading of the failure is that CentOS 7 does not have <sys/ppsclock.h> and should not be built on hosts without it. My first thought at a fix is either for waf to not build it when HAVE_SYS_PPSCLOCK_H is not defined or broaden the conditional to include the entire file.

I am also curious if this is really worth keeping. It looks like it was added in 1999 and the changes I saw in git log looked to be horizontal maintenance. Nothing specific to this file in recent times. Plus a Google search makes me think this is dead hardware.

FWIW .. this type of comment is hard to keep right.. obviously based on git log.

/*

• Check this every time you edit the code! */ #define YEAR_LAST_MODIFIED 2000

It is actually used to sanity check if a date returned is "insane" and older than the code.

Any thoughts?