wrap: do not override all external LD_LIBRARY_PATH settings
wrap: do not override all external LD_LIBRARY_PATH settings

Before this commit, all wrapped binaries will overwrite the content
of LD_LIBRARY_PATH and, therefore, fail when the required libraries can't
be found in there.

This becomes a problem in uchroot-based projects, as the environment at wrap-
time is different from the one at run-time.

simbuerg/benchbuild,simbuerg/benchbuild