Make -core/-flavor options have higher priority than linker name

Also allows -core/flavor to appear at any position in the command line.
Patch from Oleg Ranevskyy!

http://reviews.llvm.org/D5384

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@218321 91177308-0d34-0410-b5e6-96231b3b80d8