makechrootpkg: Utilize user makepkg.conf override

Created by: aplund

A user's ~/.makepkg.conf file can now be used to override settings in /etc/makepkg.conf. Inside the chroot, this can be used instead of appending to the global file. It also allows for the user options to be propogated into the chroot build. In this patch, if there is no user makepkg.conf, then the original behaviour is preserved.