scripts: don't set LD_PRELOAD with static companion libraries

When cpmpanion libraries are built statically, it is useless to set
LD_PRELOAD. Worse, it might break the build in some corner cases.

 reporter_name="Alexander BIGGA"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-06/msg00031.html"

 reporter_comment=""