...by CppunitTest setting LD_LIBRARY_PATH to include instdir/program.

This causes the spawned gpg-agent to load instdir/program/libassuan.so.0
instead of /usr/... and fail with:

writev(2, [{iov_base="gpg-agent", iov_len=9}, {iov_base=": ",
 iov_len=2}, {iov_base="relocation error", iov_len=16}, {iov_base=": ",
 iov_len=2}, {iov_base="gpg-agent", iov_len=9}, {iov_base=": ",
 iov_len=2}, {iov_base="symbol assuan_sock_set_system_ho"...,
 iov_len=118}, {iov_base="", iov_len=0}, {iov_base="", iov_len=0},
 {iov_base="\n", iov_len=1}], 10) = 159

The failure happens in the libreoffice-6-0 branch on Fedora 27, whereas
the master branch doesn't fail because it has a newer version of
libassuan that happens to provide the required symbol.

Fix this by applying the patch that was added for ASAN in
d15f042a to clear LD_LIBRARY_PATH
always on Linux.

Change-Id: I6a5c7fdfdd32234f39a182581b03d79739880c11
Reviewed-on: https://gerrit.libreoffice.org/50056Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>