Rebuild against cxxopts 3.2.0.
Simplify meson calls and adapt to packaging guidelines.
Use bash arrays with one entry per line for easier handling.
Switch to correct SPDX license identifier for project.

Signed-off-by: David Runge <dvzrv@archlinux.org>

FTR, commands used to change arch=() and then verify the changes:

$ sed -Ei "/^arch=/{s/ *?['\"]?i686['\"]? *?//;s/ *$//}" */*/PKGBUILD*

$ grep -r i686 * | grep arch= | grep -v repos

$ svn diff | grep -A 1 ^-[^-] | grep -v -- -- | cut -c2- |
  while IFS=$'\n' read -r l1; IFS=$'\n' read -r l2; do
    echo "$l1 -> $l2"
  done | sort -u