This ensures we take user specific config values for PKGDEST into
account when printing the package list. This is required as devtools
archbuild_cmd puts packages potentially into the user defined PKGDEST
which the package list would otherwise miss.
This fixes an issue with the usage of makepkg --packagelist to get the
produced artifacts filenames according to the PKGEXT used in devtools'
makepkg.conf instead of the one defined in pacman.
One goal we want to preserve is that devtools configuration should be
self contained and not require any editing of non owned files like
the host /etc/makepkg.conf to produce expected results.
Additionally modify the archbuild_cmd override for multilib builds to
use an independent variable and not fiddle with the actual arch
variable to select the appropriate cmd.
Levente Polyak