[llvm-ar] Support an options string that start with a dash

Some projects call $AR like "$AR -crs output input1 input2".

Differential Revision: https://reviews.llvm.org/D39538

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317358 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed