[clang] [HLSL][Driver][SPIRV] Add -fspv-use-legacy-buffer-matrix-order flag (PR #214575)

[Justin Bogner via cfe-commits]

bogner wrote:

I don't really like the addition of the new builtins here, and would really prefer it if we could do this using the `getpointer` path. Can we represent the transpose at the HLSL level somehow and hook this in `HLSLBuiltinTypeDeclBuilder` directly? All the new builtins are doing is transforming the new builtins to a `getpointer` and an explicit transpose anyway.

https://github.com/llvm/llvm-project/pull/214575