fixes https://github.com/llvm/llvm-project/issues/179859
For matrix types we need to check the language mode so we can change the
matrix memory layout to arrays of vectors. To make this play nice with
how the rest of clang treats matrices we need to modify the
MaybeConvertMatrixAddress and the CreateMemTemp function to know how to
reconstruct a flattened vector.
Rest of changes is just test updates.
1bb916c9af