Generalize r256026 to apply to all MachO targets, not just Darwin targets.

The PIC default is set for the MachO toolchain, not just the Darwin toolchain,
so this treats those the same. The behavior with -static should be the same
for all MachO targets. rdar://24152327

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@257556 91177308-0d34-0410-b5e6-96231b3b80d8