[Lsb-infrastructure] a couple more small bumps with the new headers

[Wichmann, Mats D]

the prototype for glBitmap needed a const qualifer
on the final argument.  I'm checking this in now.
One of the parts of the build has something with
treat-warnings-as-errors turned on so it died.
I did turn on the GL headers today by request, or
we would not be seeing this.

_POSIX_VERSION has vanished from the unistd.h hdr.
Or to be more accurate, it's LSB_VERSION < 21 only.
this kills another piece of the libbat build (which
is a cornerstone for a number of other things).

as noted in reopened bug 2051, ucontext isn't right
yet.

I'll leave more notes if there's any further info.

-- mats