GeometryShaderGen: Don't use centroid in for input variables.

[CrossVR]

No description provided.

[JosJuice]

This fixes shader compilation errors on my Intel GPU. Dolphin still freezes around the point where the shader error was before, but I don't know if that's a related problem or not, because it also happens on games that didn't have any shader errors before this PR.

[CrossVR]

@degasus Please review.

[degasus]

LGTM

[phire]

However, It creates shader compilation errors on my AMD gpu.

See Issue 8643

[Sonicadvance1]

Causes issues under catalyst in Linux, and the Nvidia proprietary driver as well.

[CrossVR]

@JosJuice Do you still have that shader dump from Intel?

[JosJuice]

http://pastie.org/10239964

[CrossVR]

Clearly fixing this on both Intel and other GPUs would require the vertex shader to have knowledge about the presence of the geometry shader. We will have to look up if the OpenGL spec really disallows the `centroid in` qualifier in the geometry shader. If it allows those qualifiers then I'll revert this change and disable the geometry shader on the affected Intel drivers.

[CrossVR]

For these inputs, "centroid in", "sample in", and interpolation
qualifiers are allowed, but are equivalent to "in".
https://www.khronos.org/registry/gles/extensions/EXT/EXT_geometry_shader.txt

Intel is not conforming to the spec.

[CrossVR]

Perhaps this behaviour is only due to interface blocks, I'll try to disable those on Intel first.