Support for -Dmacro[=defn] and -O in glslc invocation inside shader_binary() rule?

[tintor]

Macros are needed to use platform specific defines.
MoltenVK, for example, doesn't support everything from Vulkan, so #ifdef is needed in GLSL code.

[zaucy]

very true - in general more glslc flags should be supported with inspiration from cc_binary rules

[tintor]

Would you accept Pull Request which implements this?

[zaucy]

absolutely - I haven't had much time to improve this repo recently. I was sort of waiting to compelete #7 before adding extra attributes, but if you want to add extra attributes now for things like defines and includes I'm more than happy to merge that in.

Where possible it would be ideal for the attributes to behave similar to the cc_* rules.

[tintor]

Great. I have this: #44
It also implements #include