inconsistent alloca and getopt files

[Dave Love]

alloca.c and getopt.c in Emacs are different from the ones in GNU
hello, for instance.  I don't know where the canonical sources are
supposed to be now, and it's not clear to me where in the GNU
distribution one should look for copies of these and similar files to
include in other programs, but I think things should be made
consistent.

I think it would be useful to have a distribution of routines you'd
typically want to provide for when the target doesn't have (correct)
implementations, perhaps a canonical libiberty.  The Automake
distribution be a good place to have them, but I assume there's a good
reason that's not done now.