[Stackmaps] Make ithe frame-pointer required for stackmaps.

Do not eliminate the frame pointer if there is a stackmap or patchpoint in the
function. All stackmap references should be FP relative.

This fixes PR21107.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218920 91177308-0d34-0410-b5e6-96231b3b80d8