Additional LDFLAGS hacks for new shared libraries

gcc 4.9 introduces a few new shared libraries, and when we install
these into the gnu/gcclib runtime project for permanent use, we want
them to be self-referential to that MPR.  This is accomplished by
rewriting the RUNPATH using chrpath, but that requires having an
existing RUNPATH that is long enough to be edited.  These Makefile.in
hacks add additional -rpath arguments to ensure this works.
Future proofing all hooks against the 5.20 upgrade

The single most annoying change in perl5.18 (which I am skipping) was
introducing warnings for the use of experimental features.  The switch
(given/when) is my favorite new feature in perl recently, and someone
decided you needed to be warned about using it, since it was going to
change in the future.  Maybe.

This conditional no warnings like will avoid those warnings when
upgrade efsdeploy to perl5.20, which is coming soon.