sky shader example has validation eror

[fu5ha]

Related to #232, push constants when used in a "block" fashion as they are in the sky shader need a Block decoration in spir-v, I guess #232

though it does still work for me, at least on nvidia

[fu5ha]

[VZout]

The dev guide example for uniforms has the same error. And you will likely run into this as well when running ark if you enable validation.

[eddyb]

SwiftShader uses SPIRV-Tools and that also fails (see #136 (comment)) with:

SPIR-V ERROR: 0:0 PushConstant id '8' is missing Block decoration.
From Vulkan spec, section 14.5.1:
Such variables must be identified with a Block decoration
  %shared__ShaderConstants = OpTypeStruct %uint %uint %float

[eddyb]

Looks like this is easy to reproduce with:

spirv-val --target-env vulkan1.1 target/spirv-unknown-unknown/release/sky_shader.spv