[clang] [Matrix] Add a row\col major toggle in the clang driver (PR #167628)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

@cofibrant  @fhahn  I would really appreciate if we could move forward with this PR so I can start putting up more substantive changes.  I have removed all tie ins to the `-mllvm -matrix-default-layout=` with the hope that we can address that issue at a later time. For now I have four PRs blocked by this issue:
- https://github.com/llvm/llvm-project/issues/166206
 I need to be able to address multiple indexing modes for `EmitStoreThroughLValue` and `EmitLoadOfLValue` to support Vector setters via single index subscripts.
- https://github.com/llvm/llvm-project/issues/167617
Be able to change `MatrixElt` indexing schemes
- https://github.com/llvm/llvm-project/issues/166410 
 we just need to change how we consume the initailizer list
- https://github.com/llvm/llvm-project/issues/58676
 we need to add DXC specific flags that enable these clang cc1 flags

It would help me out very much if we could move forward.


https://github.com/llvm/llvm-project/pull/167628