configure: Add copyright and license block to configure.ac
Prior to copying in code from the xserver configure.ac file, it makes sense to have the license of this file clearly marked, (to show that it's licensed identically to the configure.ac file from the xserver repository). And since the text of the license refers to "the above copyright notice" it also makes sense to have an actual copyright attribution in place. I generated this list of names by looking at the output of: git shortlog -n --format=%aD -- configure.ac (and arbitrarily stopping for contributors with fewer than 15 commits). Then for each name, I looked for existing Copyright attributions in the mesa source tree with the same name, (and using "Intel Corporation" as the copyright holder where I knew that was appropriate).