Build system patches for 2019-07-02

# gpg: Signature made Wed 03 Jul 2019 12:44:28 BST
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-build-2019-07-02-v2:
  Makefile: Reuse all's recursion machinery for clean and install
  Makefile: Rename targets for make recursion
  Makefile: Drop bogus cleaning of $(ALL_SUBDIRS)/qemu-options.def
  Makefile: Remove code to smooth transition to config.status

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>