[llvm] [AMDGPU][MC] Adding symbolic name for the constant 1 over 2*pi (PR #160617)

[Jun Wang via llvm-commits]

jwanggit86 wrote:

> My $.02 is, we should align with SP3.

Well, this is not really a deviation from SP3. Using the 2 numbers for inv2pi is still supported. This allows an additional way to represent those numbers, so it's more an enhancement. Anyhow, if the reviewers don't think this should be done, I can drop it. 

https://github.com/llvm/llvm-project/pull/160617