[clang] [Driver] [NetBSD] Append -rpath for shared compiler-rt runtimes

Append appropriate -rpath when using shared compiler-rt runtimes,
e.g. '-fsanitize=address -shared-libasan'.  There's already a similar
logic in CommonArgs.cpp but it uses non-standard arch-suffixed
installation directory while we want our driver to work with standard
installation paths.

Differential Revision: https://reviews.llvm.org/D57303

llvm-svn: 352610