Optimization for vulkan1.2 emits a confusing message..

[rcoreilly]

Finally got around to looking at args to glslc and realized we weren't optimizing! Now passing the -O flag.

Now that we are optimizing, if you set the --target-env=vulkan1.2 which is appropriate, it gives a confusing error in the axon test case:

shaderc: internal error: compilation succeeded but failed to optimize: 2nd operand of Decorate: operand BufferBlock(3) requires SPIR-V version 1.3 or earlier
  OpDecorate %Neurons BufferBlock

so using 1.1 for now, but should try to figure this out. also going through the source code to fix the atomic add issue so may have some insight from there.

There is much I don't understand about these decorators and registers and whatnot. Need to read these at some point:

• https://github.com/microsoft/DirectXShaderCompiler/blob/main/docs/SPIR-V.rst

• https://www.saschawillems.de/blog/2020/05/23/shaders-for-vulkan-samples-now-also-available-in-hlsl/