[llvm] [DirectX] Infrastructure to collect shader flags for each function (PR #112967)

[S. Bharadwaj Yadavalli via llvm-commits]

bharadwajy wrote:

> We should be able to write tests that the shader flags are correct per-function by running the analysis on some IR and printing the results, which we can then check.

Added per-function test.

https://github.com/llvm/llvm-project/pull/112967