AMDGPU: Annotate necessity of flat-scratch-init

As an approximation of the existing handling to avoid
regressions. Fixes using too many registers with calls
on subtargets with the SGPR allocation bug.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308326 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed