scripts: unset LIBRARY_PATH and LPATH

These environment variables set search path for gcc at link time, which can break the build.

Signed-off-by: Erik Inge Bolsø <knan-ct@anduin.net>
Message-Id: <alpine.BSF.2.00.1205130131550.21551@anduin.net>
PatchWork-Id: 186872

reporter_name="Nye Liu"

reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

reporter_comment=""