[krbdev.mit.edu #3316] evaluate use of ELF symbol visibility pragmas for smaller code, GOT, PLT

[Sam Hartman via RT]

My personal opinion is that if we can do this in a manner where we
guarantee that the symbol visibility and export lists do not conflict
then we should do so.

We should also make sure that in cases where features we need are not
available we do not use them.

--Sam