[tlbuild] initial builds for tl'16

[Karl Berry]

    mojca (on tex-live)> whether it is expected:
    ...
    checking for freetype-config... freetype-config
    Package poppler was not found in the pkg-config search path.
    Perhaps you should add the directory containing `poppler.pc'
    to the PKG_CONFIG_PATH environment variable
    No package 'poppler' found

I've noticed that too.  I think it is expected.  Since there have been
no related reports of actual problems (that I can recall), neither Peter
nor I ever tried to trace the interactions to see if it makes any
difference.  I also think it has been happening for many years.
(Finally, if there is a problem, I doubt messing with the
PKG_CONFIG_PATH environment variable is the way to deal with it.)  -k