Using the system default 'ar' might not be the right choice when cross compiling. Don't prepend the ar options by a dash, not all ar implementations support that (llvm-ar doesn't). Also pass the 's' option when creating the merged library, to create an index. Differential Revision: https://reviews.llvm.org/D37134 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@313122 91177308-0d34-0410-b5e6-96231b3b80d8