[llvm] [AMDGPU] Add insert/extract test to test instruction V_CNDMASK_B32 (PR #79384)

[via llvm-commits]

choikwa wrote:

> The test looks OK, but what is it testing, and what does it have to do with V_CNDMASK_B32?

The test was reduced from a QUDA application with which rocm 5.5.1 was generating V_CNDMASK with an illegal operand type. This was found to be from a partial commit in attempt to reland another change. LLVM trunk no longer generates the instruction but I still thought it would be a good test to have.

https://github.com/llvm/llvm-project/pull/79384