Alternatives are specified in makepkg via (e.g.):
alternative=('sh')
There should be a file (e.g.) sh.alternative alongside the PKGBUILD containing
a list of symlinks to be created with the alternative is active. This file is
stored in the root of the package as (e.g.) .ALTERNATIVE.sh.
Signed-off-by: Allan McRae <allan@archlinux.org>