[llvm] [DirectX] Propagate shader flags mask of callees to callers (PR #118306)

[S. Bharadwaj Yadavalli via llvm-commits]

bharadwajy wrote:

> A few more comments on the algorithm. Also we should probably have a test that has an SCC of size greater than one.

Call Graph of code in `propagate-function-flags-test.ll` has an SCC with size 3. Let me know if you had some other test scenario in mind. Thanks! 

https://github.com/llvm/llvm-project/pull/118306