Merge "Add deprecation warning for base-rules-hook"

# Users can define base-rules-hook in their buildspec.mk to perform

# arbitrary operations as each module is included.

ifdef base-rules-hook

  ifndef _has_warned_about_base_rules_hook

    $(warning base-rules-hook is deprecated, please remove usages of it and/or convert to Soong.)

    _has_warned_about_base_rules_hook := true

  endif

  $(if $(base-rules-hook),)

endif