gn build: Stop passing -o to ar.

The -o flag means something different to ar than what appears to be
intended here. Also, llvm-ar doesn't accept the flag in this position.

Differential Revision: https://reviews.llvm.org/D56426

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350604 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed