Currently it's not obvious when the HLSL compiler fails, either due to a missing feature or incorrectly coded error check, which can unnecessarily complicate debugging.
It's legal for well-behaved programs to try to compile invalid shaders, but that should be a rare enough case that it's worth printing it to Wine debug output regardless.
-- v2: d3dcompiler: Print message output with ERR() in D3DPreprocess(). d3dcompiler: Print message output with ERR() in D3DCompile2().