AMDGPU: Push bitcasts through build_vector

This reduces the number of copies and reg_sequences
when using fp constant vectors. This significantly
reduces the code size in local-stack-alloc-bug.ll

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281822 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed