buildsystem: Unbreak the build (infloop) on Asterisk 11+

Apparently r408084 ( https://reviewboard.asterisk.org/r/3212/ ) broke the
build. This patch fixes it by ignoring the .lastclean dependencies if the
MENUSELECT_EMBED variable is not defined.

patches:
  tmp.diff uploaded by wdoekes (License 5674)

Review: https://reviewboard.asterisk.org/r/3228/
........

Merged revisions 408193 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@408194 f38db490-d61c-443f-a65b-d21fe96a405b