Two small changes:

+ document the difference between "A=foo make ..." and "make A=foo ..."
  and suggest using COPTS/LDOPTS if you need to use the second form to
  pass compiler and loader flags;

+ define only in one place the environment used to build stuff in menuselect/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@93558 65c4cc65-6c06-0410-ace0-fbb531ad65f3