It seems like OpenUnix's ld uses LD_LIBRARY_PATH to search for

libraries.  What's worse, the directories given in LD_LIBRARY_PATH are
checked first!  Therefore, we need a hack to prepend all the
directories we give with -L to the current value of LD_LIBRARY_PATH,
thereby temporarly forming a hacked value.

Only copy LIBEXTRAS if they are given.

Svr5 doesn't use -z allextract...