[Codegen] Change PICLevel.

We convert `Default` to `NotPIC` so that target independent code
can reason about this correctly.

Differential Revision:  http://reviews.llvm.org/D21394

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273024 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed