- how to clean up sysroot nicely without having to rebuild the cross-compiler?
  for now only removing and stowing a copy somewhere before building stage1
  helps.
- pacman with a '--no-execute-hooks' option
- makepkg with an 'alternate root' option (which doens't collide with
  pacman's options), avoids patching -r and --config into makepkg for
  stage1
- shims and provides and depends don't work yet:
  - binutils and glibc-shim
  - same for gcc-libs: glibc and gcc-libs for gcc
- bsdtar: /home/cross/i486-root/packages/i486/linux-docs-4.15.1-2-i486.pkg.tar.xz: Not found in archive
  bsdtar: /home/cross/i486-root/packages/i486/linux-headers-4.15.1-2-i486.pkg.tar.xz: Not found in archive
  bsdtar: Error exit delayed from previous errors.
  Built package linux.
- gcc PKGBUILD instead of diff
- removing all pacman databases and recreating them with repo-add, also
  removing all installed pacman packages seem a little bit paranoic. Find
  out how to speed this up and do it properly.