RFC: raise the OS baseline for systemtap.git

[Josh Stone]

(I'm not talking to myself, just relaying irc conversations...)

Frank is feeling more conservative about this, that we shouldn't
deliberately remove code that some people might still want.  He conceded
that we might just declare pre-RHEL6-ish platforms to be deprecated, no
longer actively tested, but still accepting bug reports and patches.
This would at least relieve some development burden for now.  Jonathan
added that we might set a timeline after which we can actively start
removing that old code.

I think it's likely that those deprecated platforms will bitrot and
break pretty quickly, if we're not testing them and developing with them
in mind.  But perhaps that makes it a good litmus test whether anyone
cares.  So I'd say we should deprecate them for a set period, say the
next two releases, and if we don't see pushback then we can start
actively pruning and allow things like C++11.