Use isPositionIndependent in a few more places.

Use isPositionIndependent in a few more places.

I think this converts all the simple cases that really just care about
the generated code being position independent or not. The remaining
uses are a bit more complicated and are checking things like "is this
a library or executable" or "can this symbol be preempted".

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274055 91177308-0d34-0410-b5e6-96231b3b80d8