[cmake] [libunwind] Call llvm_setup_rpath() when adding shared libraries.
[cmake] [libunwind] Call llvm_setup_rpath() when adding shared libraries.

Clang and llvm already use llvm_setup_rpath(), so this change will
help standarize rpath usage across all projects.

Differential Revision: https://reviews.llvm.org/D42461

git-svn-id: 62ef012455b6b8fcec9c41ca270ebf409aae1006@323496 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libunwind,llvm-mirror/libunwind,llvm-mirror/libunwind