Fix a stackmap bug introduced in r220710.

For a call to not return in to the stackmap shadow, the shadow must end with the call.

To do this, we must insert any required nops *before* the call, and not after it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220728 91177308-0d34-0410-b5e6-96231b3b80d8