One more follow-up to r179082 - parse PIC/PIE arguments even on platfroms that force default PIC (like Darwin x86-64), otherwise specifying -fPIC will produce bogus unused argument warning

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179092 91177308-0d34-0410-b5e6-96231b3b80d8