Add a script for generating getopt_long option tables.

Maintaining tables of long options, short options, help text and whatnot
in C code is a little bit tedious, and the simpler ways tend to cause
annoying results on modern systems that build everything in PIC mode.

So let's automate the process of building these tables from a simple
description file format, using big string arrays to reduce the amount
of relocations needed in PIC code.