always let libtool add clang library search path to pet run-time path
Ever since
pet-0.08-26-ga22f984 (link against single libLLVM
shared library when available, Wed Feb 24 14:26:25 2016 +0100),
the clang library search path has been added to the pet run-time path
if a single libLLVM shared library is found (and used),
but the clang libraries themselves may also be shared libraries and
the dynamic linker also needs to be able to find those.
Signed-off-by: Sven Verdoolaege <sven.verdoolaege@gmail.com>