Buildroot3 TODOs

- fix packages/Makefile.autotools.in to use a package-imposed patchdir
- convert all packages that use autoconf to use the infrastructure of
  packages/Makefile.autotools.in
- fix setting of flags for packages

- think about using a common --config-cache for configure
  Should take care of expanding TARGET_CONFIGURE_ARGS for cross compiles
  to working presets.