more optimizations for embedded systems:

  when LOADABLE_MODULES is off, don't export symbols from the main binary
  when LOADABLE_MODULES is off, and the compiler/linker support it, strip out code not used in the final binary


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@41166 65c4cc65-6c06-0410-ace0-fbb531ad65f3