apk with usr-merge doesn't support --root (/usr/sbin/abuild: line 529: tar: Symbolic link loop)

Analysis

• alpine's tar package has a symlink /usr/bin/tar -> /bin/tar (APKBUILD)
• Caleb's apk patches already have detection for this and don't replace tar in this case (here)
• But it does not work when apk.static gets called outside of the pmbootstrap chroot, with the --root parameter
• pmbootstrap v3 installs packages like that when running pmbootstrap build

Workaround

$ pmbootstrap -y zap
$ pmbootstrap chroot -- apk add tar
$ pmbootstrap build upower --force

Reproducer

Enable building for systemd, then:

$ pmbootstrap -y zap
$ pmbootstrap build upower --force

upower-v1.90.2.tar.bz2: OK
>>> upower: Unpacking /var/cache/distfiles/upower-v1.90.2.tar.bz2...
/usr/sbin/abuild: line 529: tar: Symbolic link loop
>>> ERROR: upower: unpack failed

Reproducer with building apk-tools from source:

#!/bin/sh -ex
BUILD_APK=0

if [ "$BUILD_APK" = 1 ]; then
	pmbootstrap -y zap -p
	pmbootstrap chroot -- apk add tar
	pmbootstrap build --src=~/code/apk-tools apk-tools
fi

pmbootstrap -y zap
# upgrade to apk built from source
pmbootstrap chroot -- sh -c 'apk add /mnt/pmbootstrap/packages/systemd-edge/x86_64/apk-tools-*.apk'
pmbootstrap build upower --force