[clang] [AMDGPU] Pack uniform float structs into vector types (PR #195417)

[Shilei Tian via cfe-commits]

shiltian wrote:

Well, we will probably need to put this on hold, since this, including the original PR, is an ABI breaking change. Not sure what would be the best way to move forward with it.

CC @t-tye 

https://github.com/llvm/llvm-project/pull/195417