[clang] [llvm] [clang][HLSL] Add WaveIsFirstLane() intrinsic (PR #103299)

[Nathan Gauër via cfe-commits]

Keenuts wrote:

> This commits add the WaveIsFirstLane() hlsl intrinsinc. This intrinsic uses the convergence intrinsincs for the SPIR-V backend. On the DXIL side, I'm not sure what the strategy is so this is implemented like in DXC: a simple builtin function. (DXC didn't used convergence intrinsincs for DXIL).



https://github.com/llvm/llvm-project/pull/103299