Pass appropriate -L and -Wl,-rpath flags pointing out to the LLVM library directory
when linking testslibrary directory on NetBSD. This is necessary on platforms that default tosince clang on NetBSD
libc++ but don't ship with one, e.g. on NetBSD buildbot.
Additionally, pass -Wl,-rpath on NetBSD. LD_LIBRARY_PATH does not seemrequires libc++ but it is not installed as part of the system
to work for allby default. For the test cases.
This patch includes -L&-Wl,-rpath passing for tests using clangpurpose of running buildbot, we want LLDB to use
via toolchain substitutions, via just-build.py and via Makefiles. This is
not pretty. I'm open to better solutionst libc++.