Merging part of r259297:

Merging part of r259297:

We need to correctly initialize the AMDGPUPromoteAlloca pass, because
later commits will add tests that try to pass the -amdgpu-promote-alloca
flag to opt.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@271591 91177308-0d34-0410-b5e6-96231b3b80d8