Fix LD_LIBRARY_PATH in GNU/Linux startup script

Fix LD_LIBRARY_PATH in GNU/Linux startup script

Currently, the startup script for GNU/Linux adds the current working directory
to LD_LIBRARY_PATH if LD_LIBRARY_PATH is not empty or unset.

For example, if LD_LIBRARY_PATH is set to "/lib" when the current script is
run, it will be set to "<install-dir>/lib::/lib", which includes the current
working directory as one of the paths.

This commit removes the extra colon added to LD_LIBRARY_PATH (without changing
the script's behavior of setting LD_LIBRARY_PATH to an empty string when it is
unset).