[cmake] [libcxxabi] 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/D42460

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@323455 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed